From ba4847e879424ad173289e8fb96cc86a09ee899b Mon Sep 17 00:00:00 2001
From: misterpoe <raymondksi@gmail.com>
Date: Fri, 5 Aug 2016 14:04:25 -0700
Subject: [PATCH] src: Node Tracing Controller

This commit adds support for trace-event tracing to Node.js. It provides
a mechanism to centralize tracing information generated by V8, Node
core, and userspace code. It includes:

 - A trace writer responsible for serializing traces and cycling the
   output files so that no individual file becomes to large.
 - A buffer for aggregating traces to allow for batched flushes.
 - An agent which initializes the tracing controller and ensures that
   trace serialization is done on a separate thread.
 - A set of macros for generating trace events.
 - Tests and documentation.

Author: Raymond Kang <raymondksi@gmail.com>
Author: Kelvin Jin <kelvinjin@google.com>
Author: Matthew Loring <mattloring@google.com>
Author: Jason Ginchereau <jasongin@microsoft.com>

PR-URL: https://github.com/nodejs/node/pull/9304

Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Josh Gavant <josh.gavant@outlook.com>
---
 doc/api/cli.md                    |   14 +
 doc/api/debugger.md               |    2 +-
 doc/api/tracing.md                |   19 +
 node.gyp                          |    5 +
 src/node.cc                       |  112 +-
 src/node.h                        |    1 +
 src/tracing/agent.cc              |   72 ++
 src/tracing/agent.h               |   31 +
 src/tracing/node_trace_buffer.cc  |  177 +++
 src/tracing/node_trace_buffer.h   |   89 ++
 src/tracing/node_trace_writer.cc  |  185 ++++
 src/tracing/node_trace_writer.h   |   74 ++
 src/tracing/trace_event.cc        |   17 +
 src/tracing/trace_event.h         | 1710 +++++++++++++++++++++++++++++
 test/parallel/test-trace-event.js |   35 +
 15 files changed, 2503 insertions(+), 40 deletions(-)
 create mode 100644 doc/api/tracing.md
 create mode 100644 src/tracing/agent.cc
 create mode 100644 src/tracing/agent.h
 create mode 100644 src/tracing/node_trace_buffer.cc
 create mode 100644 src/tracing/node_trace_buffer.h
 create mode 100644 src/tracing/node_trace_writer.cc
 create mode 100644 src/tracing/node_trace_writer.h
 create mode 100644 src/tracing/trace_event.cc
 create mode 100644 src/tracing/trace_event.h
 create mode 100644 test/parallel/test-trace-event.js

diff --git a/doc/api/cli.md b/doc/api/cli.md
index d868d70533f5f2..2000c2b3334b74 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -129,6 +129,20 @@ added: v2.1.0
 Prints a stack trace whenever synchronous I/O is detected after the first turn
 of the event loop.
 
+### `--trace-events-enabled`
+<!-- YAML
+added: REPLACEME
+-->
+
+Enables the collection of trace event tracing information.
+
+### `--trace-event-categories`
+<!-- YAML
+added: REPLACEME
+-->
+
+A comma separated list of categories that should be traced when trace event
+tracing is enabled using `--trace-events-enabled`.
 
 ### `--zero-fill-buffers`
 <!-- YAML
diff --git a/doc/api/debugger.md b/doc/api/debugger.md
index c8a61d2ce742f8..e81a0e46ea33d5 100644
--- a/doc/api/debugger.md
+++ b/doc/api/debugger.md
@@ -201,4 +201,4 @@ To start debugging, open the following URL in Chrome:
     chrome-devtools://devtools/remote/serve_file/@60cd6e859b9f557d2312f5bf532f6aec5f284980/inspector.html?experiments=true&v8only=true&ws=localhost:9229/node
 ```
 
-[TCP-based protocol]: https://github.com/v8/v8/wiki/Debugging-Protocol
+[TCP-based protocol]: https://github.com/v8/v8/wiki/Debugging-Protocol
\ No newline at end of file
diff --git a/doc/api/tracing.md b/doc/api/tracing.md
new file mode 100644
index 00000000000000..28e488201ec2d8
--- /dev/null
+++ b/doc/api/tracing.md
@@ -0,0 +1,19 @@
+# Tracing
+
+Trace Event provides a mechanism to centralize tracing information generated by
+V8, Node core, and userspace code.
+
+Tracing can be enabled by passing the `--trace-events-enabled` flag when starting a
+Node.js application.
+
+The set of categories for which traces are recorded can be specified using the
+`--trace-event-categories` flag followed by a list of comma separated category names.
+By default the `node` and `v8` categories are enabled.
+
+```txt
+node --trace-events-enabled --trace-event-categories v8,node server.js
+```
+
+Running Node.js with tracing enabled will produce log files that can be opened
+in the [`chrome://tracing`](https://www.chromium.org/developers/how-tos/trace-event-profiling-tool)
+tab of Chrome.
diff --git a/node.gyp b/node.gyp
index 8f5510d44c7366..5669091c90924a 100644
--- a/node.gyp
+++ b/node.gyp
@@ -140,6 +140,10 @@
       ],
 
       'sources': [
+        'src/tracing/agent.cc',
+        'src/tracing/node_trace_buffer.cc',
+        'src/tracing/node_trace_writer.cc',
+        'src/tracing/trace_event.cc',
         'src/debug-agent.cc',
         'src/async-wrap.cc',
         'src/env.cc',
@@ -217,6 +221,7 @@
         'src/stream_base.h',
         'src/stream_base-inl.h',
         'src/stream_wrap.h',
+        'src/tracing/trace_event.h'
         'src/tree.h',
         'src/util.h',
         'src/util-inl.h',
diff --git a/src/node.cc b/src/node.cc
index 3147a90d3e3844..1302dfed169a18 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -38,6 +38,7 @@
 #include "req-wrap.h"
 #include "req-wrap-inl.h"
 #include "string_bytes.h"
+#include "tracing/agent.h"
 #include "util.h"
 #include "uv.h"
 #if NODE_USE_V8_PLATFORM
@@ -150,6 +151,8 @@ static node_module* modpending;
 static node_module* modlist_builtin;
 static node_module* modlist_linked;
 static node_module* modlist_addon;
+static bool trace_enabled = false;
+static const char* trace_enabled_categories = nullptr;
 
 #if defined(NODE_HAVE_I18N_SUPPORT)
 // Path to ICU data (for i18n / Intl)
@@ -186,6 +189,7 @@ static uv_async_t dispatch_debug_messages_async;
 
 static Mutex node_isolate_mutex;
 static v8::Isolate* node_isolate;
+static tracing::Agent* tracing_agent;
 
 static node::DebugOptions debug_options;
 
@@ -194,6 +198,7 @@ static struct {
   void Initialize(int thread_pool_size) {
     platform_ = v8::platform::CreateDefaultPlatform(thread_pool_size);
     V8::InitializePlatform(platform_);
+    tracing::TraceEventHelper::SetCurrentPlatform(platform_);
   }
 
   void PumpMessageLoop(Isolate* isolate) {
@@ -3368,6 +3373,9 @@ void SetupProcessObject(Environment* env,
 
 void SignalExit(int signo) {
   uv_tty_reset_mode();
+  if (trace_enabled) {
+    tracing_agent->Stop();
+  }
 #ifdef __FreeBSD__
   // FreeBSD has a nasty bug, see RegisterSignalHandler for details
   struct sigaction sa;
@@ -3463,64 +3471,70 @@ static void PrintHelp() {
          "       node debug script.js [arguments] \n"
          "\n"
          "Options:\n"
-         "  -v, --version         print Node.js version\n"
-         "  -e, --eval script     evaluate script\n"
-         "  -p, --print           evaluate script and print result\n"
-         "  -c, --check           syntax check script without executing\n"
-         "  -i, --interactive     always enter the REPL even if stdin\n"
-         "                        does not appear to be a terminal\n"
-         "  -r, --require         module to preload (option can be repeated)\n"
-         "  --no-deprecation      silence deprecation warnings\n"
-         "  --trace-deprecation   show stack traces on deprecations\n"
-         "  --throw-deprecation   throw an exception anytime a deprecated "
+         "  -v, --version            print Node.js version\n"
+         "  -e, --eval script        evaluate script\n"
+         "  -p, --print              evaluate script and print result\n"
+         "  -c, --check              syntax check script without executing\n"
+         "  -i, --interactive        always enter the REPL even if stdin\n"
+         "                           does not appear to be a terminal\n"
+         "  -r, --require            module to preload (option can be "
+         "repeated)\n"
+         "  --no-deprecation         silence deprecation warnings\n"
+         "  --trace-deprecation      show stack traces on deprecations\n"
+         "  --throw-deprecation      throw an exception anytime a deprecated "
          "function is used\n"
-         "  --no-warnings         silence all process warnings\n"
-         "  --trace-warnings      show stack traces on process warnings\n"
-         "  --trace-sync-io       show stack trace when use of sync IO\n"
-         "                        is detected after the first tick\n"
-         "  --track-heap-objects  track heap object allocations for heap "
+         "  --no-warnings            silence all process warnings\n"
+         "  --trace-warnings         show stack traces on process warnings\n"
+         "  --trace-sync-io          show stack trace when use of sync IO\n"
+         "                           is detected after the first tick\n"
+         "  --trace-events-enabled   track trace events\n"
+         "  --trace-event-categories comma separated list of trace event\n"
+         "                           categories to record\n"
+         "  --track-heap-objects     track heap object allocations for heap "
          "snapshots\n"
-         "  --prof-process        process v8 profiler output generated\n"
-         "                        using --prof\n"
-         "  --zero-fill-buffers   automatically zero-fill all newly allocated\n"
-         "                        Buffer and SlowBuffer instances\n"
-         "  --v8-options          print v8 command line options\n"
-         "  --v8-pool-size=num    set v8's thread pool size\n"
+         "  --prof-process           process v8 profiler output generated\n"
+         "                           using --prof\n"
+         "  --zero-fill-buffers      automatically zero-fill all newly "
+         "allocated\n"
+         "                           Buffer and SlowBuffer instances\n"
+         "  --v8-options             print v8 command line options\n"
+         "  --v8-pool-size=num       set v8's thread pool size\n"
 #if HAVE_OPENSSL
-         "  --tls-cipher-list=val use an alternative default TLS cipher list\n"
+         "  --tls-cipher-list=val    use an alternative default TLS cipher "
+         "list\n"
 #if NODE_FIPS_MODE
-         "  --enable-fips         enable FIPS crypto at startup\n"
-         "  --force-fips          force FIPS crypto (cannot be disabled)\n"
+         "  --enable-fips            enable FIPS crypto at startup\n"
+         "  --force-fips             force FIPS crypto (cannot be disabled)\n"
 #endif  /* NODE_FIPS_MODE */
-         "  --openssl-config=path load OpenSSL configuration file from the\n"
-         "                        specified path\n"
+         "  --openssl-config=path    load OpenSSL configuration file from the\n"
+         "                           specified path\n"
 #endif /* HAVE_OPENSSL */
 #if defined(NODE_HAVE_I18N_SUPPORT)
-         "  --icu-data-dir=dir    set ICU data load path to dir\n"
-         "                        (overrides NODE_ICU_DATA)\n"
+         "  --icu-data-dir=dir       set ICU data load path to dir\n"
+         "                           (overrides NODE_ICU_DATA)\n"
 #if !defined(NODE_HAVE_SMALL_ICU)
-         "                        note: linked-in ICU data is\n"
-         "                        present.\n"
+         "                           note: linked-in ICU data is\n"
+         "                           present.\n"
 #endif
-         "  --preserve-symlinks   preserve symbolic links when resolving\n"
-         "                        and caching modules.\n"
+         "  --preserve-symlinks      preserve symbolic links when resolving\n"
+         "                           and caching modules.\n"
 #endif
          "\n"
          "Environment variables:\n"
 #ifdef _WIN32
-         "NODE_PATH                ';'-separated list of directories\n"
+         "NODE_PATH                  ';'-separated list of directories\n"
 #else
-         "NODE_PATH                ':'-separated list of directories\n"
+         "NODE_PATH                  ':'-separated list of directories\n"
 #endif
-         "                         prefixed to the module search path.\n"
-         "NODE_DISABLE_COLORS      set to 1 to disable colors in the REPL\n"
+         "                           prefixed to the module search path.\n"
+         "NODE_DISABLE_COLORS        set to 1 to disable colors in the REPL\n"
 #if defined(NODE_HAVE_I18N_SUPPORT)
-         "NODE_ICU_DATA            data path for ICU (Intl object) data\n"
+         "NODE_ICU_DATA              data path for ICU (Intl object) data\n"
 #if !defined(NODE_HAVE_SMALL_ICU)
-         "                         (will extend linked-in data)\n"
+         "                           (will extend linked-in data)\n"
 #endif
 #endif
-         "NODE_REPL_HISTORY        path to the persistent REPL history file\n"
+         "NODE_REPL_HISTORY          path to the persistent REPL history file\n"
          "\n"
          "Documentation can be found at https://nodejs.org/\n");
 }
@@ -3626,6 +3640,16 @@ static void ParseArgs(int* argc,
       trace_deprecation = true;
     } else if (strcmp(arg, "--trace-sync-io") == 0) {
       trace_sync_io = true;
+    } else if (strcmp(arg, "--trace-events-enabled") == 0) {
+      trace_enabled = true;
+    } else if (strcmp(arg, "--trace-event-categories") == 0) {
+      const char* categories = argv[index + 1];
+      if (categories == nullptr) {
+        fprintf(stderr, "%s: %s requires an argument\n", argv[0], arg);
+        exit(9);
+      }
+      args_consumed += 1;
+      trace_enabled_categories = categories;
     } else if (strcmp(arg, "--track-heap-objects") == 0) {
       track_heap_objects = true;
     } else if (strcmp(arg, "--throw-deprecation") == 0) {
@@ -4454,10 +4478,20 @@ int Start(int argc, char** argv) {
 #endif
 
   v8_platform.Initialize(v8_thread_pool_size);
+  // Enable tracing when argv has --trace-events-enabled.
+  if (trace_enabled) {
+    fprintf(stderr, "Warning: Trace event is an experimental feature "
+            "and could change at any time.\n");
+    tracing_agent = new tracing::Agent();
+    tracing_agent->Start(v8_platform.platform_, trace_enabled_categories);
+  }
   V8::Initialize();
   v8_initialized = true;
   const int exit_code =
       Start(uv_default_loop(), argc, argv, exec_argc, exec_argv);
+  if (trace_enabled) {
+    tracing_agent->Stop();
+  }
   v8_initialized = false;
   V8::Dispose();
 
diff --git a/src/node.h b/src/node.h
index 873551fa338a97..098339da1a2b9e 100644
--- a/src/node.h
+++ b/src/node.h
@@ -41,6 +41,7 @@
 
 #include "v8.h"  // NOLINT(build/include_order)
 #include "node_version.h"  // NODE_MODULE_VERSION
+#include "tracing/trace_event.h"
 
 #define NODE_MAKE_VERSION(major, minor, patch)                                \
   ((major) * 0x1000 + (minor) * 0x100 + (patch))
diff --git a/src/tracing/agent.cc b/src/tracing/agent.cc
new file mode 100644
index 00000000000000..97a3e11a2c458c
--- /dev/null
+++ b/src/tracing/agent.cc
@@ -0,0 +1,72 @@
+#include "tracing/agent.h"
+
+#include <sstream>
+#include <string>
+
+#include "env-inl.h"
+#include "libplatform/libplatform.h"
+
+namespace node {
+namespace tracing {
+
+using v8::platform::tracing::TraceConfig;
+
+Agent::Agent() {}
+
+void Agent::Start(v8::Platform* platform, const char* enabled_categories) {
+  platform_ = platform;
+
+  int err = uv_loop_init(&tracing_loop_);
+  CHECK_EQ(err, 0);
+
+  NodeTraceWriter* trace_writer = new NodeTraceWriter(&tracing_loop_);
+  TraceBuffer* trace_buffer = new NodeTraceBuffer(
+      NodeTraceBuffer::kBufferChunks, trace_writer, &tracing_loop_);
+
+  tracing_controller_ = new TracingController();
+
+  TraceConfig* trace_config = new TraceConfig();
+  if (enabled_categories) {
+    std::stringstream category_list(enabled_categories);
+    while (category_list.good()) {
+      std::string category;
+      getline(category_list, category, ',');
+      trace_config->AddIncludedCategory(category.c_str());
+    }
+  } else {
+    trace_config->AddIncludedCategory("v8");
+    trace_config->AddIncludedCategory("node");
+  }
+
+  // This thread should be created *after* async handles are created
+  // (within NodeTraceWriter and NodeTraceBuffer constructors).
+  // Otherwise the thread could shut down prematurely.
+  err = uv_thread_create(&thread_, ThreadCb, this);
+  CHECK_EQ(err, 0);
+
+  tracing_controller_->Initialize(trace_buffer);
+  tracing_controller_->StartTracing(trace_config);
+  v8::platform::SetTracingController(platform, tracing_controller_);
+}
+
+void Agent::Stop() {
+  if (!IsStarted()) {
+    return;
+  }
+  // Perform final Flush on TraceBuffer. We don't want the tracing controller
+  // to flush the buffer again on destruction of the V8::Platform.
+  tracing_controller_->StopTracing();
+  delete tracing_controller_;
+  // Thread should finish when the tracing loop is stopped.
+  uv_thread_join(&thread_);
+  v8::platform::SetTracingController(platform_, nullptr);
+}
+
+// static
+void Agent::ThreadCb(void* arg) {
+  Agent* agent = static_cast<Agent*>(arg);
+  uv_run(&agent->tracing_loop_, UV_RUN_DEFAULT);
+}
+
+}  // namespace tracing
+}  // namespace node
diff --git a/src/tracing/agent.h b/src/tracing/agent.h
new file mode 100644
index 00000000000000..098f955192e0cf
--- /dev/null
+++ b/src/tracing/agent.h
@@ -0,0 +1,31 @@
+#ifndef SRC_TRACING_AGENT_H_
+#define SRC_TRACING_AGENT_H_
+
+#include "tracing/node_trace_buffer.h"
+#include "tracing/node_trace_writer.h"
+#include "uv.h"
+#include "v8.h"
+
+namespace node {
+namespace tracing {
+
+class Agent {
+ public:
+  explicit Agent();
+  void Start(v8::Platform* platform, const char* enabled_categories);
+  void Stop();
+
+ private:
+  bool IsStarted() { return platform_ != nullptr; }
+  static void ThreadCb(void* arg);
+
+  uv_thread_t thread_;
+  uv_loop_t tracing_loop_;
+  v8::Platform* platform_ = nullptr;
+  TracingController* tracing_controller_;
+};
+
+}  // namespace tracing
+}  // namespace node
+
+#endif  // SRC_TRACING_AGENT_H_
diff --git a/src/tracing/node_trace_buffer.cc b/src/tracing/node_trace_buffer.cc
new file mode 100644
index 00000000000000..4773e08325a3ef
--- /dev/null
+++ b/src/tracing/node_trace_buffer.cc
@@ -0,0 +1,177 @@
+#include "tracing/node_trace_buffer.h"
+
+namespace node {
+namespace tracing {
+
+InternalTraceBuffer::InternalTraceBuffer(size_t max_chunks, uint32_t id,
+    NodeTraceWriter* trace_writer, NodeTraceBuffer* external_buffer)
+    : id_(id), flushing_(false), max_chunks_(max_chunks),
+      trace_writer_(trace_writer), external_buffer_(external_buffer) {
+  chunks_.resize(max_chunks);
+}
+
+TraceObject* InternalTraceBuffer::AddTraceEvent(uint64_t* handle) {
+  Mutex::ScopedLock scoped_lock(mutex_);
+  // Create new chunk if last chunk is full or there is no chunk.
+  if (total_chunks_ == 0 || chunks_[total_chunks_ - 1]->IsFull()) {
+    auto& chunk = chunks_[total_chunks_++];
+    if (chunk) {
+      chunk->Reset(current_chunk_seq_++);
+    } else {
+      chunk.reset(new TraceBufferChunk(current_chunk_seq_++));
+    }
+  }
+  auto& chunk = chunks_[total_chunks_ - 1];
+  size_t event_index;
+  TraceObject* trace_object = chunk->AddTraceEvent(&event_index);
+  *handle = MakeHandle(total_chunks_ - 1, chunk->seq(), event_index);
+  return trace_object;
+}
+
+TraceObject* InternalTraceBuffer::GetEventByHandle(uint64_t handle) {
+  Mutex::ScopedLock scoped_lock(mutex_);
+  if (handle == 0) {
+    // A handle value of zero never has a trace event associated with it.
+    return NULL;
+  }
+  size_t chunk_index, event_index;
+  uint32_t buffer_id, chunk_seq;
+  ExtractHandle(handle, &buffer_id, &chunk_index, &chunk_seq, &event_index);
+  if (buffer_id != id_ || chunk_index >= total_chunks_) {
+    // Either the chunk belongs to the other buffer, or is outside the current
+    // range of chunks loaded in memory (the latter being true suggests that
+    // the chunk has already been flushed and is no longer in memory.)
+    return NULL;
+  }
+  auto& chunk = chunks_[chunk_index];
+  if (chunk->seq() != chunk_seq) {
+    // Chunk is no longer in memory.
+    return NULL;
+  }
+  return chunk->GetEventAt(event_index);
+}
+
+void InternalTraceBuffer::Flush(bool blocking) {
+  {
+    Mutex::ScopedLock scoped_lock(mutex_);
+    if (total_chunks_ > 0) {
+      flushing_ = true;
+      for (size_t i = 0; i < total_chunks_; ++i) {
+        auto& chunk = chunks_[i];
+        for (size_t j = 0; j < chunk->size(); ++j) {
+          trace_writer_->AppendTraceEvent(chunk->GetEventAt(j));
+        }
+      }
+      total_chunks_ = 0;
+      flushing_ = false;
+    }
+  }
+  trace_writer_->Flush(blocking);
+}
+
+uint64_t InternalTraceBuffer::MakeHandle(
+    size_t chunk_index, uint32_t chunk_seq, size_t event_index) const {
+  return ((static_cast<uint64_t>(chunk_seq) * Capacity() +
+          chunk_index * TraceBufferChunk::kChunkSize + event_index) << 1) + id_;
+}
+
+void InternalTraceBuffer::ExtractHandle(
+    uint64_t handle, uint32_t* buffer_id, size_t* chunk_index,
+    uint32_t* chunk_seq, size_t* event_index) const {
+  *buffer_id = static_cast<uint32_t>(handle & 0x1);
+  handle >>= 1;
+  *chunk_seq = static_cast<uint32_t>(handle / Capacity());
+  size_t indices = handle % Capacity();
+  *chunk_index = indices / TraceBufferChunk::kChunkSize;
+  *event_index = indices % TraceBufferChunk::kChunkSize;
+}
+
+NodeTraceBuffer::NodeTraceBuffer(size_t max_chunks,
+    NodeTraceWriter* trace_writer, uv_loop_t* tracing_loop)
+    : tracing_loop_(tracing_loop), trace_writer_(trace_writer),
+      buffer1_(max_chunks, 0, trace_writer, this),
+      buffer2_(max_chunks, 1, trace_writer, this) {
+  current_buf_.store(&buffer1_);
+
+  flush_signal_.data = this;
+  int err = uv_async_init(tracing_loop_, &flush_signal_, NonBlockingFlushSignalCb);
+  CHECK_EQ(err, 0);
+
+  exit_signal_.data = this;
+  err = uv_async_init(tracing_loop_, &exit_signal_, ExitSignalCb);
+  CHECK_EQ(err, 0);
+}
+
+NodeTraceBuffer::~NodeTraceBuffer() {
+  uv_async_send(&exit_signal_);
+  Mutex::ScopedLock scoped_lock(exit_mutex_);
+  while(!exited_) {
+    exit_cond_.Wait(scoped_lock);
+  }
+}
+
+TraceObject* NodeTraceBuffer::AddTraceEvent(uint64_t* handle) {
+  // If the buffer is full, attempt to perform a flush.
+  if (!TryLoadAvailableBuffer()) {
+    // Assign a value of zero as the trace event handle.
+    // This is equivalent to calling InternalTraceBuffer::MakeHandle(0, 0, 0),
+    // and will cause GetEventByHandle to return NULL if passed as an argument.
+    *handle = 0;
+    return nullptr;
+  }
+  return current_buf_.load()->AddTraceEvent(handle);
+}
+
+TraceObject* NodeTraceBuffer::GetEventByHandle(uint64_t handle) {
+  return current_buf_.load()->GetEventByHandle(handle);
+}
+
+bool NodeTraceBuffer::Flush() {
+  buffer1_.Flush(true);
+  buffer2_.Flush(true);
+  return true;
+}
+
+// Attempts to set current_buf_ such that it references a buffer that can
+// can write at least one trace event. If both buffers are unavailable this
+// method returns false; otherwise it returns true.
+bool NodeTraceBuffer::TryLoadAvailableBuffer() {
+  InternalTraceBuffer* prev_buf = current_buf_.load();
+  if (prev_buf->IsFull()) {
+    uv_async_send(&flush_signal_); // trigger flush on a separate thread
+    InternalTraceBuffer* other_buf = prev_buf == &buffer1_ ?
+      &buffer2_ : &buffer1_;
+    if (!other_buf->IsFull()) {
+      current_buf_.store(other_buf);
+    } else {
+      return false;
+    }
+  }
+  return true;
+}
+
+// static
+void NodeTraceBuffer::NonBlockingFlushSignalCb(uv_async_t* signal) {
+  NodeTraceBuffer* buffer = reinterpret_cast<NodeTraceBuffer*>(signal->data);
+  if (buffer->buffer1_.IsFull() && !buffer->buffer1_.IsFlushing()) {
+    buffer->buffer1_.Flush(false);
+  }
+  if (buffer->buffer2_.IsFull() && !buffer->buffer2_.IsFlushing()) {
+    buffer->buffer2_.Flush(false);
+  }
+}
+
+// static
+void NodeTraceBuffer::ExitSignalCb(uv_async_t* signal) {
+  NodeTraceBuffer* buffer = reinterpret_cast<NodeTraceBuffer*>(signal->data);
+  uv_close(reinterpret_cast<uv_handle_t*>(&buffer->flush_signal_), nullptr);
+  uv_close(reinterpret_cast<uv_handle_t*>(&buffer->exit_signal_), [](uv_handle_t* signal) {
+      NodeTraceBuffer* buffer = reinterpret_cast<NodeTraceBuffer*>(signal->data);
+      Mutex::ScopedLock scoped_lock(buffer->exit_mutex_);
+      buffer->exited_ = true;
+      buffer->exit_cond_.Signal(scoped_lock);
+  });
+}
+
+}  // namespace tracing
+}  // namespace node
diff --git a/src/tracing/node_trace_buffer.h b/src/tracing/node_trace_buffer.h
new file mode 100644
index 00000000000000..619799fdb21978
--- /dev/null
+++ b/src/tracing/node_trace_buffer.h
@@ -0,0 +1,89 @@
+#ifndef SRC_NODE_TRACE_BUFFER_H_
+#define SRC_NODE_TRACE_BUFFER_H_
+
+#include "node_mutex.h"
+#include "tracing/node_trace_writer.h"
+#include "libplatform/v8-tracing.h"
+
+#include <atomic>
+
+namespace node {
+namespace tracing {
+
+using v8::platform::tracing::TraceBuffer;
+using v8::platform::tracing::TraceBufferChunk;
+using v8::platform::tracing::TraceObject;
+
+// forward declaration
+class NodeTraceBuffer;
+
+class InternalTraceBuffer {
+ public:
+  InternalTraceBuffer(size_t max_chunks, uint32_t id,
+                      NodeTraceWriter* trace_writer,
+                      NodeTraceBuffer* external_buffer);
+
+  TraceObject* AddTraceEvent(uint64_t* handle);
+  TraceObject* GetEventByHandle(uint64_t handle);
+  void Flush(bool blocking);
+  bool IsFull() const {
+    return total_chunks_ == max_chunks_ && chunks_[total_chunks_ - 1]->IsFull();
+  }
+  bool IsFlushing() const {
+    return flushing_;
+  }
+
+ private:
+  uint64_t MakeHandle(size_t chunk_index, uint32_t chunk_seq,
+                      size_t event_index) const;
+  void ExtractHandle(uint64_t handle, uint32_t* buffer_id, size_t* chunk_index,
+                     uint32_t* chunk_seq, size_t* event_index) const;
+  size_t Capacity() const { return max_chunks_ * TraceBufferChunk::kChunkSize; }
+
+  Mutex mutex_;
+  bool flushing_;
+  size_t max_chunks_;
+  NodeTraceWriter* trace_writer_;
+  NodeTraceBuffer* external_buffer_;
+  std::vector<std::unique_ptr<TraceBufferChunk>> chunks_;
+  size_t total_chunks_ = 0;
+  uint32_t current_chunk_seq_ = 1;
+  uint32_t id_;
+};
+
+class NodeTraceBuffer : public TraceBuffer {
+ public:
+  NodeTraceBuffer(size_t max_chunks, NodeTraceWriter* trace_writer,
+                  uv_loop_t* tracing_loop);
+  ~NodeTraceBuffer();
+
+  TraceObject* AddTraceEvent(uint64_t* handle) override;
+  TraceObject* GetEventByHandle(uint64_t handle) override;
+  bool Flush() override;
+
+  static const size_t kBufferChunks = 1024;
+
+ private:
+  bool TryLoadAvailableBuffer();
+  static void NonBlockingFlushSignalCb(uv_async_t* signal);
+  static void ExitSignalCb(uv_async_t* signal);
+
+  uv_loop_t* tracing_loop_;
+  uv_async_t flush_signal_;
+  uv_async_t exit_signal_;
+  bool exited_ = false;
+  // Used exclusively for exit logic.
+  Mutex exit_mutex_;
+  // Used to wait until async handles have been closed.
+  ConditionVariable exit_cond_;
+  std::unique_ptr<NodeTraceWriter> trace_writer_;
+  // TODO: Change std::atomic to something less contentious.
+  std::atomic<InternalTraceBuffer*> current_buf_;
+  InternalTraceBuffer buffer1_;
+  InternalTraceBuffer buffer2_;
+};
+
+}  // namespace tracing
+}  // namespace node
+
+#endif  // SRC_NODE_TRACING_CONTROLLER_H_
diff --git a/src/tracing/node_trace_writer.cc b/src/tracing/node_trace_writer.cc
new file mode 100644
index 00000000000000..41753c5e65e557
--- /dev/null
+++ b/src/tracing/node_trace_writer.cc
@@ -0,0 +1,185 @@
+#include "tracing/node_trace_writer.h"
+
+#include <string.h>
+#include <fcntl.h>
+
+#include "util.h"
+
+namespace node {
+namespace tracing {
+
+NodeTraceWriter::NodeTraceWriter(uv_loop_t* tracing_loop)
+    : tracing_loop_(tracing_loop) {
+  flush_signal_.data = this;
+  int err = uv_async_init(tracing_loop_, &flush_signal_, FlushSignalCb);
+  CHECK_EQ(err, 0);
+
+  exit_signal_.data = this;
+  err = uv_async_init(tracing_loop_, &exit_signal_, ExitSignalCb);
+  CHECK_EQ(err, 0);
+}
+
+void NodeTraceWriter::WriteSuffix() {
+  // If our final log file has traces, then end the file appropriately.
+  // This means that if no trace events are recorded, then no trace file is
+  // produced.
+  bool should_flush = false;
+  {
+    Mutex::ScopedLock scoped_lock(stream_mutex_);
+    if (total_traces_ > 0) {
+      total_traces_ = 0; // so we don't write it again in FlushPrivate
+      // Appends "]}" to stream_.
+      delete json_trace_writer_;
+      should_flush = true;
+    }
+  }
+  if (should_flush) {
+    Flush(true);
+  }
+}
+
+NodeTraceWriter::~NodeTraceWriter() {
+  WriteSuffix();
+  uv_fs_t req;
+  int err;
+  if (fd_ != -1) {
+    err = uv_fs_close(tracing_loop_, &req, fd_, nullptr);
+    CHECK_EQ(err, 0);
+    uv_fs_req_cleanup(&req);
+  }
+  uv_async_send(&exit_signal_);
+  Mutex::ScopedLock scoped_lock(request_mutex_);
+  while(!exited_) {
+    exit_cond_.Wait(scoped_lock);
+  }
+}
+
+void NodeTraceWriter::OpenNewFileForStreaming() {
+  ++file_num_;
+  uv_fs_t req;
+  std::ostringstream log_file;
+  log_file << "node_trace." << file_num_ << ".log";
+  fd_ = uv_fs_open(tracing_loop_, &req, log_file.str().c_str(),
+      O_CREAT | O_WRONLY | O_TRUNC, 0644, NULL);
+  CHECK_NE(fd_, -1);
+  uv_fs_req_cleanup(&req);
+}
+
+void NodeTraceWriter::AppendTraceEvent(TraceObject* trace_event) {
+  Mutex::ScopedLock scoped_lock(stream_mutex_);
+  // If this is the first trace event, open a new file for streaming.
+  if (total_traces_ == 0) {
+    OpenNewFileForStreaming();
+    // Constructing a new JSONTraceWriter object appends "{\"traceEvents\":["
+    // to stream_.
+    // In other words, the constructor initializes the serialization stream
+    // to a state where we can start writing trace events to it.
+    // Repeatedly constructing and destroying json_trace_writer_ allows
+    // us to use V8's JSON writer instead of implementing our own.
+    json_trace_writer_ = TraceWriter::CreateJSONTraceWriter(stream_);
+  }
+  ++total_traces_;
+  json_trace_writer_->AppendTraceEvent(trace_event);
+}
+
+void NodeTraceWriter::FlushPrivate() {
+  std::string str;
+  int highest_request_id;
+  {
+    Mutex::ScopedLock stream_scoped_lock(stream_mutex_);
+    if (total_traces_ >= kTracesPerFile) {
+      total_traces_ = 0;
+      // Destroying the member JSONTraceWriter object appends "]}" to
+      // stream_ - in other words, ending a JSON file.
+      delete json_trace_writer_;
+    }
+    // str() makes a copy of the contents of the stream.
+    str = stream_.str();
+    stream_.str("");
+    stream_.clear();
+  }
+  {
+    Mutex::ScopedLock request_scoped_lock(request_mutex_);
+    highest_request_id = num_write_requests_;
+  }
+  WriteToFile(std::move(str), highest_request_id);
+}
+
+void NodeTraceWriter::FlushSignalCb(uv_async_t* signal) {
+  NodeTraceWriter* trace_writer = static_cast<NodeTraceWriter*>(signal->data);
+  trace_writer->FlushPrivate();
+}
+
+// TODO: Remove (is it necessary to change the API? Since because of WriteSuffix
+// it no longer matters whether it's true or false)
+void NodeTraceWriter::Flush() {
+  Flush(true);
+}
+
+void NodeTraceWriter::Flush(bool blocking) {
+  Mutex::ScopedLock scoped_lock(request_mutex_);
+  if (!json_trace_writer_) {
+    return;
+  }
+  int request_id = ++num_write_requests_;
+  int err = uv_async_send(&flush_signal_);
+  CHECK_EQ(err, 0);
+  if (blocking) {
+    // Wait until data associated with this request id has been written to disk.
+    // This guarantees that data from all earlier requests have also been
+    // written.
+    while (request_id > highest_request_id_completed_) {
+      request_cond_.Wait(scoped_lock);
+    }
+  }
+}
+
+void NodeTraceWriter::WriteToFile(std::string&& str, int highest_request_id) {
+  WriteRequest* write_req = new WriteRequest();
+  write_req->str = std::move(str);
+  write_req->writer = this;
+  write_req->highest_request_id = highest_request_id;
+  uv_buf_t uv_buf = uv_buf_init(const_cast<char*>(write_req->str.c_str()),
+      write_req->str.length());
+  request_mutex_.Lock();
+  // Manage a queue of WriteRequest objects because the behavior of uv_write is
+  // is undefined if the same WriteRequest object is used more than once
+  // between WriteCb calls. In addition, this allows us to keep track of the id
+  // of the latest write request that actually been completed.
+  write_req_queue_.push(write_req);
+  request_mutex_.Unlock();
+  int err = uv_fs_write(tracing_loop_, reinterpret_cast<uv_fs_t*>(write_req),
+      fd_, &uv_buf, 1, -1, WriteCb);
+  CHECK_EQ(err, 0);
+}
+
+void NodeTraceWriter::WriteCb(uv_fs_t* req) {
+  WriteRequest* write_req = reinterpret_cast<WriteRequest*>(req);
+  CHECK_GE(write_req->req.result, 0);
+
+  NodeTraceWriter* writer = write_req->writer;
+  int highest_request_id = write_req->highest_request_id;
+  {
+    Mutex::ScopedLock scoped_lock(writer->request_mutex_);
+    CHECK_EQ(write_req, writer->write_req_queue_.front());
+    writer->write_req_queue_.pop();
+    writer->highest_request_id_completed_ = highest_request_id;
+    writer->request_cond_.Broadcast(scoped_lock);
+  }
+  delete write_req;
+}
+
+// static
+void NodeTraceWriter::ExitSignalCb(uv_async_t* signal) {
+  NodeTraceWriter* trace_writer = static_cast<NodeTraceWriter*>(signal->data);
+  uv_close(reinterpret_cast<uv_handle_t*>(&trace_writer->flush_signal_), nullptr);
+  uv_close(reinterpret_cast<uv_handle_t*>(&trace_writer->exit_signal_), [](uv_handle_t* signal) {
+      NodeTraceWriter* trace_writer = static_cast<NodeTraceWriter*>(signal->data);
+      Mutex::ScopedLock scoped_lock(trace_writer->request_mutex_);
+      trace_writer->exited_ = true;
+      trace_writer->exit_cond_.Signal(scoped_lock);
+  });
+}
+
+}  // namespace tracing
+}  // namespace node
diff --git a/src/tracing/node_trace_writer.h b/src/tracing/node_trace_writer.h
new file mode 100644
index 00000000000000..5813db0ab1fd33
--- /dev/null
+++ b/src/tracing/node_trace_writer.h
@@ -0,0 +1,74 @@
+#ifndef SRC_NODE_TRACE_WRITER_H_
+#define SRC_NODE_TRACE_WRITER_H_
+
+#include <sstream>
+#include <queue>
+
+#include "node_mutex.h"
+#include "libplatform/v8-tracing.h"
+#include "uv.h"
+
+namespace node {
+namespace tracing {
+
+using v8::platform::tracing::TraceObject;
+using v8::platform::tracing::TraceWriter;
+using v8::platform::tracing::TracingController;
+
+class NodeTraceWriter : public TraceWriter {
+ public:
+  NodeTraceWriter(uv_loop_t* tracing_loop);
+  ~NodeTraceWriter();
+
+  void AppendTraceEvent(TraceObject* trace_event) override;
+  void Flush() override;
+  void Flush(bool blocking);
+
+  static const int kTracesPerFile = 1 << 19;
+
+ private:
+  struct WriteRequest {
+    uv_fs_t req;
+    NodeTraceWriter* writer;
+    std::string str;
+    int highest_request_id;
+  };
+
+  static void WriteCb(uv_fs_t* req);
+  void OpenNewFileForStreaming();
+  void WriteToFile(std::string&& str, int highest_request_id);
+  void WriteSuffix();
+  static void FlushSignalCb(uv_async_t* signal);
+  void FlushPrivate();
+  static void ExitSignalCb(uv_async_t* signal);
+
+  uv_loop_t* tracing_loop_;
+  // Triggers callback to initiate writing the contents of stream_ to disk.
+  uv_async_t flush_signal_;
+  // Triggers callback to close async objects, ending the tracing thread.
+  uv_async_t exit_signal_;
+  // Prevents concurrent R/W on state related to serialized trace data
+  // before it's written to disk, namely stream_ and total_traces_.
+  Mutex stream_mutex_;
+  // Prevents concurrent R/W on state related to write requests.
+  Mutex request_mutex_;
+  // Allows blocking calls to Flush() to wait on a condition for
+  // trace events to be written to disk.
+  ConditionVariable request_cond_;
+  // Used to wait until async handles have been closed.
+  ConditionVariable exit_cond_;
+  int fd_ = -1;
+  std::queue<WriteRequest*> write_req_queue_;
+  int num_write_requests_ = 0;
+  int highest_request_id_completed_ = 0;
+  int total_traces_ = 0;
+  int file_num_ = 0;
+  std::ostringstream stream_;
+  TraceWriter* json_trace_writer_ = nullptr;
+  bool exited_ = false;
+};
+
+}  // namespace tracing
+}  // namespace node
+
+#endif  // SRC_NODE_TRACE_WRITER_H_
diff --git a/src/tracing/trace_event.cc b/src/tracing/trace_event.cc
new file mode 100644
index 00000000000000..b83cae6e05c10c
--- /dev/null
+++ b/src/tracing/trace_event.cc
@@ -0,0 +1,17 @@
+#include "tracing/trace_event.h"
+
+namespace node {
+namespace tracing {
+
+v8::Platform* platform_ = nullptr;
+
+void TraceEventHelper::SetCurrentPlatform(v8::Platform* platform) {
+  platform_ = platform;
+}
+
+v8::Platform* TraceEventHelper::GetCurrentPlatform() {
+  return platform_;
+}
+
+}  // namespace tracing
+}  // namespace node
diff --git a/src/tracing/trace_event.h b/src/tracing/trace_event.h
new file mode 100644
index 00000000000000..a035fd51500bb9
--- /dev/null
+++ b/src/tracing/trace_event.h
@@ -0,0 +1,1710 @@
+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SRC_TRACING_TRACE_EVENT_H_
+#define SRC_TRACING_TRACE_EVENT_H_
+
+#include <stddef.h>
+
+#include "v8-platform.h"
+
+// This header file defines implementation details of how the trace macros in
+// trace_event_common.h collect and store trace events. Anything not
+// implementation-specific should go in trace_macros_common.h instead of here.
+
+// From v8/base/trace_event/common/trace_event_common.h
+
+// This header file defines the set of trace_event macros without specifying
+// how the events actually get collected and stored. If you need to expose trace
+// events to some other universe, you can copy-and-paste this file as well as
+// trace_event.h, modifying the macros contained there as necessary for the
+// target platform. The end result is that multiple libraries can funnel events
+// through to a shared trace event collector.
+
+// IMPORTANT: To avoid conflicts, if you need to modify this file for a library,
+// land your change in base/ first, and then copy-and-paste it.
+
+// Trace events are for tracking application performance and resource usage.
+// Macros are provided to track:
+//    Begin and end of function calls
+//    Counters
+//
+// Events are issued against categories. Whereas LOG's
+// categories are statically defined, TRACE categories are created
+// implicitly with a string. For example:
+//   TRACE_EVENT_INSTANT0("MY_SUBSYSTEM", "SomeImportantEvent",
+//                        TRACE_EVENT_SCOPE_THREAD)
+//
+// It is often the case that one trace may belong in multiple categories at the
+// same time. The first argument to the trace can be a comma-separated list of
+// categories, forming a category group, like:
+//
+// TRACE_EVENT_INSTANT0("input,views", "OnMouseOver", TRACE_EVENT_SCOPE_THREAD)
+//
+// We can enable/disable tracing of OnMouseOver by enabling/disabling either
+// category.
+//
+// Events can be INSTANT, or can be pairs of BEGIN and END in the same scope:
+//   TRACE_EVENT_BEGIN0("MY_SUBSYSTEM", "SomethingCostly")
+//   doSomethingCostly()
+//   TRACE_EVENT_END0("MY_SUBSYSTEM", "SomethingCostly")
+// Note: our tools can't always determine the correct BEGIN/END pairs unless
+// these are used in the same scope. Use ASYNC_BEGIN/ASYNC_END macros if you
+// need them to be in separate scopes.
+//
+// A common use case is to trace entire function scopes. This
+// issues a trace BEGIN and END automatically:
+//   void doSomethingCostly() {
+//     TRACE_EVENT0("MY_SUBSYSTEM", "doSomethingCostly");
+//     ...
+//   }
+//
+// Additional parameters can be associated with an event:
+//   void doSomethingCostly2(int howMuch) {
+//     TRACE_EVENT1("MY_SUBSYSTEM", "doSomethingCostly",
+//         "howMuch", howMuch);
+//     ...
+//   }
+//
+// The trace system will automatically add to this information the
+// current process id, thread id, and a timestamp in microseconds.
+//
+// To trace an asynchronous procedure such as an IPC send/receive, use
+// ASYNC_BEGIN and ASYNC_END:
+//   [single threaded sender code]
+//     static int send_count = 0;
+//     ++send_count;
+//     TRACE_EVENT_ASYNC_BEGIN0("ipc", "message", send_count);
+//     Send(new MyMessage(send_count));
+//   [receive code]
+//     void OnMyMessage(send_count) {
+//       TRACE_EVENT_ASYNC_END0("ipc", "message", send_count);
+//     }
+// The third parameter is a unique ID to match ASYNC_BEGIN/ASYNC_END pairs.
+// ASYNC_BEGIN and ASYNC_END can occur on any thread of any traced process.
+// Pointers can be used for the ID parameter, and they will be mangled
+// internally so that the same pointer on two different processes will not
+// match. For example:
+//   class MyTracedClass {
+//    public:
+//     MyTracedClass() {
+//       TRACE_EVENT_ASYNC_BEGIN0("category", "MyTracedClass", this);
+//     }
+//     ~MyTracedClass() {
+//       TRACE_EVENT_ASYNC_END0("category", "MyTracedClass", this);
+//     }
+//   }
+//
+// Trace event also supports counters, which is a way to track a quantity
+// as it varies over time. Counters are created with the following macro:
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter", g_myCounterValue);
+//
+// Counters are process-specific. The macro itself can be issued from any
+// thread, however.
+//
+// Sometimes, you want to track two counters at once. You can do this with two
+// counter macros:
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter0", g_myCounterValue[0]);
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter1", g_myCounterValue[1]);
+// Or you can do it with a combined macro:
+//   TRACE_COUNTER2("MY_SUBSYSTEM", "myCounter",
+//       "bytesPinned", g_myCounterValue[0],
+//       "bytesAllocated", g_myCounterValue[1]);
+// This indicates to the tracing UI that these counters should be displayed
+// in a single graph, as a summed area chart.
+//
+// Since counters are in a global namespace, you may want to disambiguate with a
+// unique ID, by using the TRACE_COUNTER_ID* variations.
+//
+// By default, trace collection is compiled in, but turned off at runtime.
+// Collecting trace data is the responsibility of the embedding
+// application. In Chrome's case, navigating to about:tracing will turn on
+// tracing and display data collected across all active processes.
+//
+//
+// Memory scoping note:
+// Tracing copies the pointers, not the string content, of the strings passed
+// in for category_group, name, and arg_names.  Thus, the following code will
+// cause problems:
+//     char* str = strdup("importantName");
+//     TRACE_EVENT_INSTANT0("SUBSYSTEM", str);  // BAD!
+//     free(str);                   // Trace system now has dangling pointer
+//
+// To avoid this issue with the |name| and |arg_name| parameters, use the
+// TRACE_EVENT_COPY_XXX overloads of the macros at additional runtime overhead.
+// Notes: The category must always be in a long-lived char* (i.e. static const).
+//        The |arg_values|, when used, are always deep copied with the _COPY
+//        macros.
+//
+// When are string argument values copied:
+// const char* arg_values are only referenced by default:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", "literal string is only referenced");
+// Use TRACE_STR_COPY to force copying of a const char*:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", TRACE_STR_COPY("string will be copied"));
+// std::string arg_values are always copied:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", std::string("string will be copied"));
+//
+//
+// Convertable notes:
+// Converting a large data type to a string can be costly. To help with this,
+// the trace framework provides an interface ConvertableToTraceFormat. If you
+// inherit from it and implement the AppendAsTraceFormat method the trace
+// framework will call back to your object to convert a trace output time. This
+// means, if the category for the event is disabled, the conversion will not
+// happen.
+//
+//   class MyData : public base::trace_event::ConvertableToTraceFormat {
+//    public:
+//     MyData() {}
+//     void AppendAsTraceFormat(std::string* out) const override {
+//       out->append("{\"foo\":1}");
+//     }
+//    private:
+//     ~MyData() override {}
+//     DISALLOW_COPY_AND_ASSIGN(MyData);
+//   };
+//
+//   TRACE_EVENT1("foo", "bar", "data",
+//                std::unique_ptr<ConvertableToTraceFormat>(new MyData()));
+//
+// The trace framework will take ownership if the passed pointer and it will
+// be free'd when the trace buffer is flushed.
+//
+// Note, we only do the conversion when the buffer is flushed, so the provided
+// data object should not be modified after it's passed to the trace framework.
+//
+//
+// Thread Safety:
+// A thread safe singleton and mutex are used for thread safety. Category
+// enabled flags are used to limit the performance impact when the system
+// is not enabled.
+//
+// TRACE_EVENT macros first cache a pointer to a category. The categories are
+// statically allocated and safe at all times, even after exit. Fetching a
+// category is protected by the TraceLog::lock_. Multiple threads initializing
+// the static variable is safe, as they will be serialized by the lock and
+// multiple calls will return the same pointer to the category.
+//
+// Then the category_group_enabled flag is checked. This is a unsigned char, and
+// not intended to be multithread safe. It optimizes access to AddTraceEvent
+// which is threadsafe internally via TraceLog::lock_. The enabled flag may
+// cause some threads to incorrectly call or skip calling AddTraceEvent near
+// the time of the system being enabled or disabled. This is acceptable as
+// we tolerate some data loss while the system is being enabled/disabled and
+// because AddTraceEvent is threadsafe internally and checks the enabled state
+// again under lock.
+//
+// Without the use of these static category pointers and enabled flags all
+// trace points would carry a significant performance cost of acquiring a lock
+// and resolving the category.
+
+#if defined(TRACE_EVENT0)
+#error "Another copy of this file has already been included."
+#endif
+
+// This will mark the trace event as disabled by default. The user will need
+// to explicitly enable the event.
+#define TRACE_DISABLED_BY_DEFAULT(name) "disabled-by-default-" name
+
+// Records a pair of begin and end events called "name" for the current
+// scope, with 0, 1 or 2 associated arguments. If the category is not
+// enabled, then this does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT0(category_group, name)    \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name)
+#define TRACE_EVENT_WITH_FLOW0(category_group, name, bind_id, flow_flags)  \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED_WITH_FLOW(category_group, name, bind_id, \
+                                            flow_flags)
+#define TRACE_EVENT1(category_group, name, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name, arg1_name, arg1_val)
+#define TRACE_EVENT_WITH_FLOW1(category_group, name, bind_id, flow_flags,  \
+                               arg1_name, arg1_val)                        \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED_WITH_FLOW(category_group, name, bind_id, \
+                                            flow_flags, arg1_name, arg1_val)
+#define TRACE_EVENT2(category_group, name, arg1_name, arg1_val, arg2_name,   \
+                     arg2_val)                                               \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name, arg1_name, arg1_val, \
+                                  arg2_name, arg2_val)
+#define TRACE_EVENT_WITH_FLOW2(category_group, name, bind_id, flow_flags,    \
+                               arg1_name, arg1_val, arg2_name, arg2_val)     \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED_WITH_FLOW(category_group, name, bind_id,   \
+                                            flow_flags, arg1_name, arg1_val, \
+                                            arg2_name, arg2_val)
+
+// UNSHIPPED_TRACE_EVENT* are like TRACE_EVENT* except that they are not
+// included in official builds.
+
+#if OFFICIAL_BUILD
+#undef TRACING_IS_OFFICIAL_BUILD
+#define TRACING_IS_OFFICIAL_BUILD 1
+#elif !defined(TRACING_IS_OFFICIAL_BUILD)
+#define TRACING_IS_OFFICIAL_BUILD 0
+#endif
+
+#if TRACING_IS_OFFICIAL_BUILD
+#define UNSHIPPED_TRACE_EVENT0(category_group, name) (void)0
+#define UNSHIPPED_TRACE_EVENT1(category_group, name, arg1_name, arg1_val) \
+  (void)0
+#define UNSHIPPED_TRACE_EVENT2(category_group, name, arg1_name, arg1_val, \
+                               arg2_name, arg2_val)                       \
+  (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT0(category_group, name, scope) (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT1(category_group, name, scope, arg1_name, \
+                                       arg1_val)                               \
+  (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT2(category_group, name, scope, arg1_name, \
+                                       arg1_val, arg2_name, arg2_val)          \
+  (void)0
+#else
+#define UNSHIPPED_TRACE_EVENT0(category_group, name) \
+  TRACE_EVENT0(category_group, name)
+#define UNSHIPPED_TRACE_EVENT1(category_group, name, arg1_name, arg1_val) \
+  TRACE_EVENT1(category_group, name, arg1_name, arg1_val)
+#define UNSHIPPED_TRACE_EVENT2(category_group, name, arg1_name, arg1_val, \
+                               arg2_name, arg2_val)                       \
+  TRACE_EVENT2(category_group, name, arg1_name, arg1_val, arg2_name, arg2_val)
+#define UNSHIPPED_TRACE_EVENT_INSTANT0(category_group, name, scope) \
+  TRACE_EVENT_INSTANT0(category_group, name, scope)
+#define UNSHIPPED_TRACE_EVENT_INSTANT1(category_group, name, scope, arg1_name, \
+                                       arg1_val)                               \
+  TRACE_EVENT_INSTANT1(category_group, name, scope, arg1_name, arg1_val)
+#define UNSHIPPED_TRACE_EVENT_INSTANT2(category_group, name, scope, arg1_name, \
+                                       arg1_val, arg2_name, arg2_val)          \
+  TRACE_EVENT_INSTANT2(category_group, name, scope, arg1_name, arg1_val,       \
+                       arg2_name, arg2_val)
+#endif
+
+// Records a single event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_INSTANT0(category_group, name, scope)                   \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE | scope)
+#define TRACE_EVENT_INSTANT1(category_group, name, scope, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name,    \
+                           TRACE_EVENT_FLAG_NONE | scope, arg1_name, arg1_val)
+#define TRACE_EVENT_INSTANT2(category_group, name, scope, arg1_name, arg1_val, \
+                             arg2_name, arg2_val)                              \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name,    \
+                           TRACE_EVENT_FLAG_NONE | scope, arg1_name, arg1_val, \
+                           arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_INSTANT0(category_group, name, scope)              \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY | scope)
+#define TRACE_EVENT_COPY_INSTANT1(category_group, name, scope, arg1_name,   \
+                                  arg1_val)                                 \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY | scope, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_INSTANT2(category_group, name, scope, arg1_name,      \
+                                  arg1_val, arg2_name, arg2_val)               \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name,    \
+                           TRACE_EVENT_FLAG_COPY | scope, arg1_name, arg1_val, \
+                           arg2_name, arg2_val)
+
+#define TRACE_EVENT_INSTANT_WITH_TIMESTAMP0(category_group, name, scope, \
+                                            timestamp)                   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                    \
+      TRACE_EVENT_PHASE_INSTANT, category_group, name, 0, 0, timestamp,  \
+      TRACE_EVENT_FLAG_NONE | scope)
+
+// Syntactic sugars for the sampling tracing in the main thread.
+#define TRACE_EVENT_SCOPED_SAMPLING_STATE(category, name) \
+  TRACE_EVENT_SCOPED_SAMPLING_STATE_FOR_BUCKET(0, category, name)
+#define TRACE_EVENT_GET_SAMPLING_STATE() \
+  TRACE_EVENT_GET_SAMPLING_STATE_FOR_BUCKET(0)
+#define TRACE_EVENT_SET_SAMPLING_STATE(category, name) \
+  TRACE_EVENT_SET_SAMPLING_STATE_FOR_BUCKET(0, category, name)
+#define TRACE_EVENT_SET_NONCONST_SAMPLING_STATE(categoryAndName) \
+  TRACE_EVENT_SET_NONCONST_SAMPLING_STATE_FOR_BUCKET(0, categoryAndName)
+
+// Records a single BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_BEGIN0(category_group, name)                          \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_BEGIN1(category_group, name, arg1_name, arg1_val)     \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_BEGIN2(category_group, name, arg1_name, arg1_val,     \
+                           arg2_name, arg2_val)                           \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val,    \
+                           arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_BEGIN0(category_group, name)                     \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_BEGIN1(category_group, name, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name,  \
+                           TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_BEGIN2(category_group, name, arg1_name, arg1_val, \
+                                arg2_name, arg2_val)                       \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name,  \
+                           TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val,     \
+                           arg2_name, arg2_val)
+
+// Similar to TRACE_EVENT_BEGINx but with a custom |at| timestamp provided.
+// - |id| is used to match the _BEGIN event with the _END event.
+//   Events are considered to match if their category_group, name and id values
+//   all match. |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+#define TRACE_EVENT_BEGIN_WITH_ID_TID_AND_TIMESTAMP0(category_group, name, id, \
+                                                     thread_id, timestamp)     \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id, thread_id,      \
+      timestamp, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_COPY_BEGIN_WITH_ID_TID_AND_TIMESTAMP0(                \
+    category_group, name, id, thread_id, timestamp)                       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                     \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id, thread_id, \
+      timestamp, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_BEGIN_WITH_ID_TID_AND_TIMESTAMP1(                \
+    category_group, name, id, thread_id, timestamp, arg1_name, arg1_val)  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                     \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id, thread_id, \
+      timestamp, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_BEGIN_WITH_ID_TID_AND_TIMESTAMP2(                \
+    category_group, name, id, thread_id, timestamp, arg1_name, arg1_val,  \
+    arg2_name, arg2_val)                                                  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                     \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id, thread_id, \
+      timestamp, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, arg2_name,   \
+      arg2_val)
+
+// Records a single END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_END0(category_group, name)                          \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_END1(category_group, name, arg1_name, arg1_val)     \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_END2(category_group, name, arg1_name, arg1_val, arg2_name, \
+                         arg2_val)                                             \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name,        \
+                           TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val,         \
+                           arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_END0(category_group, name)                     \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_END1(category_group, name, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name,  \
+                           TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_END2(category_group, name, arg1_name, arg1_val, \
+                              arg2_name, arg2_val)                       \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name,  \
+                           TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val,   \
+                           arg2_name, arg2_val)
+
+#define TRACE_EVENT_MARK_WITH_TIMESTAMP1(category_group, name, timestamp, \
+                                         arg1_name, arg1_val)             \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                     \
+      TRACE_EVENT_PHASE_MARK, category_group, name, 0, 0, timestamp,      \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+
+#define TRACE_EVENT_COPY_MARK(category_group, name)                      \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_MARK, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY)
+
+#define TRACE_EVENT_COPY_MARK_WITH_TIMESTAMP(category_group, name, timestamp) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                         \
+      TRACE_EVENT_PHASE_MARK, category_group, name, 0, 0, timestamp,          \
+      TRACE_EVENT_FLAG_COPY)
+
+// Similar to TRACE_EVENT_ENDx but with a custom |at| timestamp provided.
+// - |id| is used to match the _BEGIN event with the _END event.
+//   Events are considered to match if their category_group, name and id values
+//   all match. |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+#define TRACE_EVENT_END_WITH_ID_TID_AND_TIMESTAMP0(category_group, name, id, \
+                                                   thread_id, timestamp)     \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                        \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id, thread_id,      \
+      timestamp, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_COPY_END_WITH_ID_TID_AND_TIMESTAMP0(                \
+    category_group, name, id, thread_id, timestamp)                     \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                   \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id, thread_id, \
+      timestamp, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_END_WITH_ID_TID_AND_TIMESTAMP1(                 \
+    category_group, name, id, thread_id, timestamp, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                    \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id, thread_id,  \
+      timestamp, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_END_WITH_ID_TID_AND_TIMESTAMP2(                 \
+    category_group, name, id, thread_id, timestamp, arg1_name, arg1_val, \
+    arg2_name, arg2_val)                                                 \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                    \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id, thread_id,  \
+      timestamp, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, arg2_name,  \
+      arg2_val)
+
+// Records the value of a counter called "name" immediately. Value
+// must be representable as a 32 bit integer.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_COUNTER1(category_group, name, value)                         \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, "value",                  \
+                           static_cast<int>(value))
+#define TRACE_COPY_COUNTER1(category_group, name, value)                    \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY, "value",                  \
+                           static_cast<int>(value))
+
+// Records the values of a multi-parted counter called "name" immediately.
+// The UI will treat value1 and value2 as parts of a whole, displaying their
+// values as a stacked-bar chart.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_COUNTER2(category_group, name, value1_name, value1_val,       \
+                       value2_name, value2_val)                             \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, value1_name,              \
+                           static_cast<int>(value1_val), value2_name,       \
+                           static_cast<int>(value2_val))
+#define TRACE_COPY_COUNTER2(category_group, name, value1_name, value1_val,  \
+                            value2_name, value2_val)                        \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY, value1_name,              \
+                           static_cast<int>(value1_val), value2_name,       \
+                           static_cast<int>(value2_val))
+
+// Similar to TRACE_COUNTERx, but with a custom |timestamp| provided.
+#define TRACE_COUNTER_WITH_TIMESTAMP1(category_group, name, timestamp, value) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_TIMESTAMP(                                    \
+      TRACE_EVENT_PHASE_COUNTER, category_group, name, timestamp,             \
+      TRACE_EVENT_FLAG_NONE, "value", static_cast<int>(value))
+
+#define TRACE_COUNTER_WITH_TIMESTAMP2(category_group, name, timestamp,      \
+                                      value1_name, value1_val, value2_name, \
+                                      value2_val)                           \
+  INTERNAL_TRACE_EVENT_ADD_WITH_TIMESTAMP(                                  \
+      TRACE_EVENT_PHASE_COUNTER, category_group, name, timestamp,           \
+      TRACE_EVENT_FLAG_NONE, value1_name, static_cast<int>(value1_val),     \
+      value2_name, static_cast<int>(value2_val))
+
+// Records the value of a counter called "name" immediately. Value
+// must be representable as a 32 bit integer.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to disambiguate counters with the same name. It must either
+//   be a pointer or an integer value up to 64 bits. If it's a pointer, the bits
+//   will be xored with a hash of the process ID so that the same pointer on
+//   two different processes will not collide.
+#define TRACE_COUNTER_ID1(category_group, name, id, value)                    \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE, "value",  \
+                                   static_cast<int>(value))
+#define TRACE_COPY_COUNTER_ID1(category_group, name, id, value)               \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY, "value",  \
+                                   static_cast<int>(value))
+
+// Records the values of a multi-parted counter called "name" immediately.
+// The UI will treat value1 and value2 as parts of a whole, displaying their
+// values as a stacked-bar chart.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to disambiguate counters with the same name. It must either
+//   be a pointer or an integer value up to 64 bits. If it's a pointer, the bits
+//   will be xored with a hash of the process ID so that the same pointer on
+//   two different processes will not collide.
+#define TRACE_COUNTER_ID2(category_group, name, id, value1_name, value1_val,  \
+                          value2_name, value2_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE,           \
+                                   value1_name, static_cast<int>(value1_val), \
+                                   value2_name, static_cast<int>(value2_val))
+#define TRACE_COPY_COUNTER_ID2(category_group, name, id, value1_name,         \
+                               value1_val, value2_name, value2_val)           \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY,           \
+                                   value1_name, static_cast<int>(value1_val), \
+                                   value2_name, static_cast<int>(value2_val))
+
+// TRACE_EVENT_SAMPLE_* events are injected by the sampling profiler.
+#define TRACE_EVENT_SAMPLE_WITH_TID_AND_TIMESTAMP0(category_group, name,       \
+                                                   thread_id, timestamp)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_SAMPLE, category_group, name, 0, thread_id, timestamp, \
+      TRACE_EVENT_FLAG_NONE)
+
+#define TRACE_EVENT_SAMPLE_WITH_TID_AND_TIMESTAMP1(                            \
+    category_group, name, thread_id, timestamp, arg1_name, arg1_val)           \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_SAMPLE, category_group, name, 0, thread_id, timestamp, \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+
+#define TRACE_EVENT_SAMPLE_WITH_TID_AND_TIMESTAMP2(category_group, name,       \
+                                                   thread_id, timestamp,       \
+                                                   arg1_name, arg1_val,        \
+                                                   arg2_name, arg2_val)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_SAMPLE, category_group, name, 0, thread_id, timestamp, \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// ASYNC_STEP_* APIs should be only used by legacy code. New code should
+// consider using NESTABLE_ASYNC_* APIs to describe substeps within an async
+// event.
+// Records a single ASYNC_BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to match the ASYNC_BEGIN event with the ASYNC_END event. ASYNC
+//   events are considered to match if their category_group, name and id values
+//   all match. |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+//
+// An asynchronous operation can consist of multiple phases. The first phase is
+// defined by the ASYNC_BEGIN calls. Additional phases can be defined using the
+// ASYNC_STEP_INTO or ASYNC_STEP_PAST macros. The ASYNC_STEP_INTO macro will
+// annotate the block following the call. The ASYNC_STEP_PAST macro will
+// annotate the block prior to the call. Note that any particular event must use
+// only STEP_INTO or STEP_PAST macros; they can not mix and match. When the
+// operation completes, call ASYNC_END.
+//
+// An ASYNC trace typically occurs on a single thread (if not, they will only be
+// drawn on the thread defined in the ASYNC_BEGIN event), but all events in that
+// operation must use the same |name| and |id|. Each step can have its own
+// args.
+#define TRACE_EVENT_ASYNC_BEGIN0(category_group, name, id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+                                   category_group, name, id,      \
+                                   TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ASYNC_BEGIN1(category_group, name, id, arg1_name, \
+                                 arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN,     \
+                                   category_group, name, id,          \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_ASYNC_BEGIN2(category_group, name, id, arg1_name, \
+                                 arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                   \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id,        \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN0(category_group, name, id)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+                                   category_group, name, id,      \
+                                   TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN1(category_group, name, id, arg1_name, \
+                                      arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN,          \
+                                   category_group, name, id,               \
+                                   TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN2(category_group, name, id, arg1_name, \
+                                      arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                        \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id,             \
+      TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Similar to TRACE_EVENT_ASYNC_BEGINx but with a custom |at| timestamp
+// provided.
+#define TRACE_EVENT_ASYNC_BEGIN_WITH_TIMESTAMP0(category_group, name, id, \
+                                                timestamp)                \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                     \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id,            \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ASYNC_BEGIN_WITH_TIMESTAMP1(                           \
+    category_group, name, id, timestamp, arg1_name, arg1_val)              \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                      \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id,             \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE, \
+      arg1_name, arg1_val)
+#define TRACE_EVENT_ASYNC_BEGIN_WITH_TIMESTAMP2(category_group, name, id,      \
+                                                timestamp, arg1_name,          \
+                                                arg1_val, arg2_name, arg2_val) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id,                 \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE,     \
+      arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN_WITH_TIMESTAMP0(category_group, name, id, \
+                                                     timestamp)                \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id,                 \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_COPY)
+
+// Records a single ASYNC_STEP_INTO event for |step| immediately. If the
+// category is not enabled, then this does nothing. The |name| and |id| must
+// match the ASYNC_BEGIN event above. The |step| param identifies this step
+// within the async event. This should be called at the beginning of the next
+// phase of an asynchronous operation. The ASYNC_BEGIN event must not have any
+// ASYNC_STEP_PAST events.
+#define TRACE_EVENT_ASYNC_STEP_INTO0(category_group, name, id, step)  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP_INTO, \
+                                   category_group, name, id,          \
+                                   TRACE_EVENT_FLAG_NONE, "step", step)
+#define TRACE_EVENT_ASYNC_STEP_INTO1(category_group, name, id, step, \
+                                     arg1_name, arg1_val)            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
+      TRACE_EVENT_PHASE_ASYNC_STEP_INTO, category_group, name, id,   \
+      TRACE_EVENT_FLAG_NONE, "step", step, arg1_name, arg1_val)
+
+// Similar to TRACE_EVENT_ASYNC_STEP_INTOx but with a custom |at| timestamp
+// provided.
+#define TRACE_EVENT_ASYNC_STEP_INTO_WITH_TIMESTAMP0(category_group, name, id, \
+                                                    step, timestamp)          \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                         \
+      TRACE_EVENT_PHASE_ASYNC_STEP_INTO, category_group, name, id,            \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE,    \
+      "step", step)
+
+// Records a single ASYNC_STEP_PAST event for |step| immediately. If the
+// category is not enabled, then this does nothing. The |name| and |id| must
+// match the ASYNC_BEGIN event above. The |step| param identifies this step
+// within the async event. This should be called at the beginning of the next
+// phase of an asynchronous operation. The ASYNC_BEGIN event must not have any
+// ASYNC_STEP_INTO events.
+#define TRACE_EVENT_ASYNC_STEP_PAST0(category_group, name, id, step)  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP_PAST, \
+                                   category_group, name, id,          \
+                                   TRACE_EVENT_FLAG_NONE, "step", step)
+#define TRACE_EVENT_ASYNC_STEP_PAST1(category_group, name, id, step, \
+                                     arg1_name, arg1_val)            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
+      TRACE_EVENT_PHASE_ASYNC_STEP_PAST, category_group, name, id,   \
+      TRACE_EVENT_FLAG_NONE, "step", step, arg1_name, arg1_val)
+
+// Records a single ASYNC_END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+#define TRACE_EVENT_ASYNC_END0(category_group, name, id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+                                   category_group, name, id,    \
+                                   TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ASYNC_END1(category_group, name, id, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END,               \
+                                   category_group, name, id,                  \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_ASYNC_END2(category_group, name, id, arg1_name, arg1_val, \
+                               arg2_name, arg2_val)                           \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                           \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id,                  \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_ASYNC_END0(category_group, name, id)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+                                   category_group, name, id,    \
+                                   TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_ASYNC_END1(category_group, name, id, arg1_name, \
+                                    arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END,          \
+                                   category_group, name, id,             \
+                                   TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_ASYNC_END2(category_group, name, id, arg1_name, \
+                                    arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                      \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id,             \
+      TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Similar to TRACE_EVENT_ASYNC_ENDx but with a custom |at| timestamp provided.
+#define TRACE_EVENT_ASYNC_END_WITH_TIMESTAMP0(category_group, name, id, \
+                                              timestamp)                \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                   \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id,            \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ASYNC_END_WITH_TIMESTAMP1(category_group, name, id,       \
+                                              timestamp, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                         \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id,                  \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE,    \
+      arg1_name, arg1_val)
+#define TRACE_EVENT_ASYNC_END_WITH_TIMESTAMP2(category_group, name, id,       \
+                                              timestamp, arg1_name, arg1_val, \
+                                              arg2_name, arg2_val)            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                         \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id,                  \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE,    \
+      arg1_name, arg1_val, arg2_name, arg2_val)
+
+// NESTABLE_ASYNC_* APIs are used to describe an async operation, which can
+// be nested within a NESTABLE_ASYNC event and/or have inner NESTABLE_ASYNC
+// events.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - A pair of NESTABLE_ASYNC_BEGIN event and NESTABLE_ASYNC_END event is
+//   considered as a match if their category_group, name and id all match.
+// - |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+// - |id| is used to match a child NESTABLE_ASYNC event with its parent
+//   NESTABLE_ASYNC event. Therefore, events in the same nested event tree must
+//   be logged using the same id and category_group.
+//
+// Unmatched NESTABLE_ASYNC_END event will be parsed as an event that starts
+// at the first NESTABLE_ASYNC event of that id, and unmatched
+// NESTABLE_ASYNC_BEGIN event will be parsed as an event that ends at the last
+// NESTABLE_ASYNC event of that id. Corresponding warning messages for
+// unmatched events will be shown in the analysis view.
+
+// Records a single NESTABLE_ASYNC_BEGIN event called "name" immediately, with
+// 0, 1 or 2 associated arguments. If the category is not enabled, then this
+// does nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_BEGIN0(category_group, name, id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN, \
+                                   category_group, name, id,               \
+                                   TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_NESTABLE_ASYNC_BEGIN1(category_group, name, id, arg1_name, \
+                                          arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN,     \
+                                   category_group, name, id,                   \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_NESTABLE_ASYNC_BEGIN2(category_group, name, id, arg1_name, \
+                                          arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                            \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN, category_group, name, id,        \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+// Records a single NESTABLE_ASYNC_END event called "name" immediately, with 0
+// or 2 associated arguments. If the category is not enabled, then this does
+// nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_END0(category_group, name, id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_NESTABLE_ASYNC_END, \
+                                   category_group, name, id,             \
+                                   TRACE_EVENT_FLAG_NONE)
+// Records a single NESTABLE_ASYNC_END event called "name" immediately, with 1
+// associated argument. If the category is not enabled, then this does nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_END1(category_group, name, id, arg1_name, \
+                                        arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_NESTABLE_ASYNC_END,     \
+                                   category_group, name, id,                 \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_NESTABLE_ASYNC_END2(category_group, name, id, arg1_name, \
+                                        arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                          \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_END, category_group, name, id,        \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Records a single NESTABLE_ASYNC_INSTANT event called "name" immediately,
+// with one associated argument. If the category is not enabled, then this
+// does nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_INSTANT1(category_group, name, id,        \
+                                            arg1_name, arg1_val)             \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_NESTABLE_ASYNC_INSTANT, \
+                                   category_group, name, id,                 \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+// Records a single NESTABLE_ASYNC_INSTANT event called "name" immediately,
+// with 2 associated arguments. If the category is not enabled, then this
+// does nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_INSTANT2(                              \
+    category_group, name, id, arg1_name, arg1_val, arg2_name, arg2_val)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                       \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_INSTANT, category_group, name, id, \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+
+#define TRACE_EVENT_COPY_NESTABLE_ASYNC_BEGIN_WITH_TTS2(                       \
+    category_group, name, id, arg1_name, arg1_val, arg2_name, arg2_val)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                            \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN, category_group, name, id,        \
+      TRACE_EVENT_FLAG_ASYNC_TTS | TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, \
+      arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_NESTABLE_ASYNC_END_WITH_TTS2(                         \
+    category_group, name, id, arg1_name, arg1_val, arg2_name, arg2_val)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                            \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_END, category_group, name, id,          \
+      TRACE_EVENT_FLAG_ASYNC_TTS | TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, \
+      arg2_name, arg2_val)
+
+// Similar to TRACE_EVENT_NESTABLE_ASYNC_{BEGIN,END}x but with a custom
+// |timestamp| provided.
+#define TRACE_EVENT_NESTABLE_ASYNC_BEGIN_WITH_TIMESTAMP0(category_group, name, \
+                                                         id, timestamp)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN, category_group, name, id,        \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE)
+
+#define TRACE_EVENT_NESTABLE_ASYNC_END_WITH_TIMESTAMP0(category_group, name, \
+                                                       id, timestamp)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                        \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_END, category_group, name, id,        \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE)
+
+#define TRACE_EVENT_COPY_NESTABLE_ASYNC_BEGIN_WITH_TIMESTAMP0(          \
+    category_group, name, id, timestamp)                                \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                   \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN, category_group, name, id, \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_NESTABLE_ASYNC_END_WITH_TIMESTAMP0(          \
+    category_group, name, id, timestamp)                              \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                 \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_END, category_group, name, id, \
+      TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_COPY)
+
+// Records a single NESTABLE_ASYNC_INSTANT event called "name" immediately,
+// with 2 associated arguments. If the category is not enabled, then this
+// does nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_INSTANT2(                              \
+    category_group, name, id, arg1_name, arg1_val, arg2_name, arg2_val)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                       \
+      TRACE_EVENT_PHASE_NESTABLE_ASYNC_INSTANT, category_group, name, id, \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Records a single FLOW_BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to match the FLOW_BEGIN event with the FLOW_END event. FLOW
+//   events are considered to match if their category_group, name and id values
+//   all match. |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+// FLOW events are different from ASYNC events in how they are drawn by the
+// tracing UI. A FLOW defines asynchronous data flow, such as posting a task
+// (FLOW_BEGIN) and later executing that task (FLOW_END). Expect FLOWs to be
+// drawn as lines or arrows from FLOW_BEGIN scopes to FLOW_END scopes. Similar
+// to ASYNC, a FLOW can consist of multiple phases. The first phase is defined
+// by the FLOW_BEGIN calls. Additional phases can be defined using the FLOW_STEP
+// macros. When the operation completes, call FLOW_END. An async operation can
+// span threads and processes, but all events in that operation must use the
+// same |name| and |id|. Each event can have its own args.
+#define TRACE_EVENT_FLOW_BEGIN0(category_group, name, id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+                                   category_group, name, id,     \
+                                   TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_FLOW_BEGIN1(category_group, name, id, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN,               \
+                                   category_group, name, id,                   \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_FLOW_BEGIN2(category_group, name, id, arg1_name, arg1_val, \
+                                arg2_name, arg2_val)                           \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                            \
+      TRACE_EVENT_PHASE_FLOW_BEGIN, category_group, name, id,                  \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_FLOW_BEGIN0(category_group, name, id)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+                                   category_group, name, id,     \
+                                   TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_FLOW_BEGIN1(category_group, name, id, arg1_name, \
+                                     arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN,          \
+                                   category_group, name, id,              \
+                                   TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_FLOW_BEGIN2(category_group, name, id, arg1_name, \
+                                     arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                       \
+      TRACE_EVENT_PHASE_FLOW_BEGIN, category_group, name, id,             \
+      TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Records a single FLOW_STEP event for |step| immediately. If the category
+// is not enabled, then this does nothing. The |name| and |id| must match the
+// FLOW_BEGIN event above. The |step| param identifies this step within the
+// async event. This should be called at the beginning of the next phase of an
+// asynchronous operation.
+#define TRACE_EVENT_FLOW_STEP0(category_group, name, id, step)  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_STEP, \
+                                   category_group, name, id,    \
+                                   TRACE_EVENT_FLAG_NONE, "step", step)
+#define TRACE_EVENT_FLOW_STEP1(category_group, name, id, step, arg1_name, \
+                               arg1_val)                                  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                       \
+      TRACE_EVENT_PHASE_FLOW_STEP, category_group, name, id,              \
+      TRACE_EVENT_FLAG_NONE, "step", step, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_FLOW_STEP0(category_group, name, id, step) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_STEP,     \
+                                   category_group, name, id,        \
+                                   TRACE_EVENT_FLAG_COPY, "step", step)
+#define TRACE_EVENT_COPY_FLOW_STEP1(category_group, name, id, step, arg1_name, \
+                                    arg1_val)                                  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                            \
+      TRACE_EVENT_PHASE_FLOW_STEP, category_group, name, id,                   \
+      TRACE_EVENT_FLAG_COPY, "step", step, arg1_name, arg1_val)
+
+// Records a single FLOW_END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+#define TRACE_EVENT_FLOW_END0(category_group, name, id)                        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_FLOW_END_BIND_TO_ENCLOSING0(category_group, name, id)      \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id,                                   \
+                                   TRACE_EVENT_FLAG_BIND_TO_ENCLOSING)
+#define TRACE_EVENT_FLOW_END1(category_group, name, id, arg1_name, arg1_val)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE, arg1_name, \
+                                   arg1_val)
+#define TRACE_EVENT_FLOW_END2(category_group, name, id, arg1_name, arg1_val,   \
+                              arg2_name, arg2_val)                             \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE, arg1_name, \
+                                   arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_FLOW_END0(category_group, name, id)                   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_FLOW_END1(category_group, name, id, arg1_name,        \
+                                   arg1_val)                                   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY, arg1_name, \
+                                   arg1_val)
+#define TRACE_EVENT_COPY_FLOW_END2(category_group, name, id, arg1_name,        \
+                                   arg1_val, arg2_name, arg2_val)              \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY, arg1_name, \
+                                   arg1_val, arg2_name, arg2_val)
+
+// Special trace event macro to trace task execution with the location where it
+// was posted from.
+#define TRACE_TASK_EXECUTION(run_function, task) \
+  INTERNAL_TRACE_TASK_EXECUTION(run_function, task)
+
+// TRACE_EVENT_METADATA* events are information related to other
+// injected events, not events in their own right.
+#define TRACE_EVENT_METADATA1(category_group, name, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_METADATA_ADD(category_group, name, arg1_name, arg1_val)
+
+// Records a clock sync event.
+#define TRACE_EVENT_CLOCK_SYNC_RECEIVER(sync_id)                               \
+  INTERNAL_TRACE_EVENT_ADD(                                                    \
+      TRACE_EVENT_PHASE_CLOCK_SYNC, "__metadata", "clock_sync",                \
+      TRACE_EVENT_FLAG_NONE, "sync_id", sync_id)
+#define TRACE_EVENT_CLOCK_SYNC_ISSUER(sync_id, issue_ts, issue_end_ts)         \
+  INTERNAL_TRACE_EVENT_ADD_WITH_TIMESTAMP(                                     \
+      TRACE_EVENT_PHASE_CLOCK_SYNC, "__metadata", "clock_sync",                \
+      issue_end_ts.ToInternalValue(), TRACE_EVENT_FLAG_NONE,                   \
+      "sync_id", sync_id, "issue_ts", issue_ts.ToInternalValue())
+
+// Macros to track the life time and value of arbitrary client objects.
+// See also TraceTrackableObject.
+#define TRACE_EVENT_OBJECT_CREATED_WITH_ID(category_group, name, id) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
+      TRACE_EVENT_PHASE_CREATE_OBJECT, category_group, name,         \
+      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE)
+
+#define TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(category_group, name, id, \
+                                            snapshot)                 \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                   \
+      TRACE_EVENT_PHASE_SNAPSHOT_OBJECT, category_group, name,        \
+      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE, "snapshot", snapshot)
+
+#define TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID_AND_TIMESTAMP(                    \
+    category_group, name, id, timestamp, snapshot)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                         \
+      TRACE_EVENT_PHASE_SNAPSHOT_OBJECT, category_group, name,                \
+      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, \
+      TRACE_EVENT_FLAG_NONE, "snapshot", snapshot)
+
+#define TRACE_EVENT_OBJECT_DELETED_WITH_ID(category_group, name, id) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
+      TRACE_EVENT_PHASE_DELETE_OBJECT, category_group, name,         \
+      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE)
+
+// Records entering and leaving trace event contexts. |category_group| and
+// |name| specify the context category and type. |context| is a
+// snapshotted context object id.
+#define TRACE_EVENT_ENTER_CONTEXT(category_group, name, context) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                              \
+      TRACE_EVENT_PHASE_ENTER_CONTEXT, category_group, name,     \
+      TRACE_ID_DONT_MANGLE(context), TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_LEAVE_CONTEXT(category_group, name, context) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                              \
+      TRACE_EVENT_PHASE_LEAVE_CONTEXT, category_group, name,     \
+      TRACE_ID_DONT_MANGLE(context), TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_SCOPED_CONTEXT(category_group, name, context) \
+  INTERNAL_TRACE_EVENT_SCOPED_CONTEXT(category_group, name,       \
+                                      TRACE_ID_DONT_MANGLE(context))
+
+// Macro to specify that two trace IDs are identical. For example,
+// TRACE_BIND_IDS(
+//     "category", "name",
+//     TRACE_ID_WITH_SCOPE("net::URLRequest", 0x1000),
+//     TRACE_ID_WITH_SCOPE("blink::ResourceFetcher::FetchRequest", 0x2000))
+// tells the trace consumer that events with ID ("net::URLRequest", 0x1000) from
+// the current process have the same ID as events with ID
+// ("blink::ResourceFetcher::FetchRequest", 0x2000).
+#define TRACE_BIND_IDS(category_group, name, id, bind_id) \
+  INTERNAL_TRACE_EVENT_ADD_BIND_IDS(category_group, name, id, bind_id);
+
+// Macro to efficiently determine if a given category group is enabled.
+#define TRACE_EVENT_CATEGORY_GROUP_ENABLED(category_group, ret)             \
+  do {                                                                      \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                 \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
+      *ret = true;                                                          \
+    } else {                                                                \
+      *ret = false;                                                         \
+    }                                                                       \
+  } while (0)
+
+// Macro to explicitly warm up a given category group. This could be useful in
+// cases where we want to initialize a category group before any trace events
+// for that category group is reported. For example, to have a category group
+// always show up in the "record categories" list for manually selecting
+// settings in about://tracing.
+#define TRACE_EVENT_WARMUP_CATEGORY(category_group) \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group)
+
+// Macro to efficiently determine, through polling, if a new trace has begun.
+#define TRACE_EVENT_IS_NEW_TRACE(ret)                                      \
+  do {                                                                     \
+    static int INTERNAL_TRACE_EVENT_UID(lastRecordingNumber) = 0;          \
+    int num_traces_recorded = TRACE_EVENT_API_GET_NUM_TRACES_RECORDED();   \
+    if (num_traces_recorded != -1 &&                                       \
+        num_traces_recorded !=                                             \
+            INTERNAL_TRACE_EVENT_UID(lastRecordingNumber)) {               \
+      INTERNAL_TRACE_EVENT_UID(lastRecordingNumber) = num_traces_recorded; \
+      *ret = true;                                                         \
+    } else {                                                               \
+      *ret = false;                                                        \
+    }                                                                      \
+  } while (0)
+
+// Notes regarding the following definitions:
+// New values can be added and propagated to third party libraries, but existing
+// definitions must never be changed, because third party libraries may use old
+// definitions.
+
+// Phase indicates the nature of an event entry. E.g. part of a begin/end pair.
+#define TRACE_EVENT_PHASE_BEGIN ('B')
+#define TRACE_EVENT_PHASE_END ('E')
+#define TRACE_EVENT_PHASE_COMPLETE ('X')
+#define TRACE_EVENT_PHASE_INSTANT ('I')
+#define TRACE_EVENT_PHASE_ASYNC_BEGIN ('S')
+#define TRACE_EVENT_PHASE_ASYNC_STEP_INTO ('T')
+#define TRACE_EVENT_PHASE_ASYNC_STEP_PAST ('p')
+#define TRACE_EVENT_PHASE_ASYNC_END ('F')
+#define TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN ('b')
+#define TRACE_EVENT_PHASE_NESTABLE_ASYNC_END ('e')
+#define TRACE_EVENT_PHASE_NESTABLE_ASYNC_INSTANT ('n')
+#define TRACE_EVENT_PHASE_FLOW_BEGIN ('s')
+#define TRACE_EVENT_PHASE_FLOW_STEP ('t')
+#define TRACE_EVENT_PHASE_FLOW_END ('f')
+#define TRACE_EVENT_PHASE_METADATA ('M')
+#define TRACE_EVENT_PHASE_COUNTER ('C')
+#define TRACE_EVENT_PHASE_SAMPLE ('P')
+#define TRACE_EVENT_PHASE_CREATE_OBJECT ('N')
+#define TRACE_EVENT_PHASE_SNAPSHOT_OBJECT ('O')
+#define TRACE_EVENT_PHASE_DELETE_OBJECT ('D')
+#define TRACE_EVENT_PHASE_MEMORY_DUMP ('v')
+#define TRACE_EVENT_PHASE_MARK ('R')
+#define TRACE_EVENT_PHASE_CLOCK_SYNC ('c')
+#define TRACE_EVENT_PHASE_ENTER_CONTEXT ('(')
+#define TRACE_EVENT_PHASE_LEAVE_CONTEXT (')')
+#define TRACE_EVENT_PHASE_BIND_IDS ('=')
+
+// Flags for changing the behavior of TRACE_EVENT_API_ADD_TRACE_EVENT.
+#define TRACE_EVENT_FLAG_NONE (static_cast<unsigned int>(0))
+#define TRACE_EVENT_FLAG_COPY (static_cast<unsigned int>(1 << 0))
+#define TRACE_EVENT_FLAG_HAS_ID (static_cast<unsigned int>(1 << 1))
+#define TRACE_EVENT_FLAG_MANGLE_ID (static_cast<unsigned int>(1 << 2))
+#define TRACE_EVENT_FLAG_SCOPE_OFFSET (static_cast<unsigned int>(1 << 3))
+#define TRACE_EVENT_FLAG_SCOPE_EXTRA (static_cast<unsigned int>(1 << 4))
+#define TRACE_EVENT_FLAG_EXPLICIT_TIMESTAMP (static_cast<unsigned int>(1 << 5))
+#define TRACE_EVENT_FLAG_ASYNC_TTS (static_cast<unsigned int>(1 << 6))
+#define TRACE_EVENT_FLAG_BIND_TO_ENCLOSING (static_cast<unsigned int>(1 << 7))
+#define TRACE_EVENT_FLAG_FLOW_IN (static_cast<unsigned int>(1 << 8))
+#define TRACE_EVENT_FLAG_FLOW_OUT (static_cast<unsigned int>(1 << 9))
+#define TRACE_EVENT_FLAG_HAS_CONTEXT_ID (static_cast<unsigned int>(1 << 10))
+#define TRACE_EVENT_FLAG_HAS_PROCESS_ID (static_cast<unsigned int>(1 << 11))
+
+#define TRACE_EVENT_FLAG_SCOPE_MASK                          \
+  (static_cast<unsigned int>(TRACE_EVENT_FLAG_SCOPE_OFFSET | \
+                             TRACE_EVENT_FLAG_SCOPE_EXTRA))
+
+// Type values for identifying types in the TraceValue union.
+#define TRACE_VALUE_TYPE_BOOL (static_cast<unsigned char>(1))
+#define TRACE_VALUE_TYPE_UINT (static_cast<unsigned char>(2))
+#define TRACE_VALUE_TYPE_INT (static_cast<unsigned char>(3))
+#define TRACE_VALUE_TYPE_DOUBLE (static_cast<unsigned char>(4))
+#define TRACE_VALUE_TYPE_POINTER (static_cast<unsigned char>(5))
+#define TRACE_VALUE_TYPE_STRING (static_cast<unsigned char>(6))
+#define TRACE_VALUE_TYPE_COPY_STRING (static_cast<unsigned char>(7))
+#define TRACE_VALUE_TYPE_CONVERTABLE (static_cast<unsigned char>(8))
+
+// Enum reflecting the scope of an INSTANT event. Must fit within
+// TRACE_EVENT_FLAG_SCOPE_MASK.
+#define TRACE_EVENT_SCOPE_GLOBAL (static_cast<unsigned char>(0 << 3))
+#define TRACE_EVENT_SCOPE_PROCESS (static_cast<unsigned char>(1 << 3))
+#define TRACE_EVENT_SCOPE_THREAD (static_cast<unsigned char>(2 << 3))
+
+#define TRACE_EVENT_SCOPE_NAME_GLOBAL ('g')
+#define TRACE_EVENT_SCOPE_NAME_PROCESS ('p')
+#define TRACE_EVENT_SCOPE_NAME_THREAD ('t')
+
+
+// The pointer returned from GetCategoryGroupEnabled() points to a
+// value with zero or more of the following bits. Used in this class only.
+// The TRACE_EVENT macros should only use the value as a bool.
+// These values must be in sync with macro values in trace_log.h in
+// chromium.
+enum CategoryGroupEnabledFlags {
+  // Category group enabled for the recording mode.
+  kEnabledForRecording_CategoryGroupEnabledFlags = 1 << 0,
+  // Category group enabled by SetEventCallbackEnabled().
+  kEnabledForEventCallback_CategoryGroupEnabledFlags = 1 << 2,
+  // Category group enabled to export events to ETW.
+  kEnabledForETWExport_CategoryGroupEnabledFlags = 1 << 3,
+};
+
+// By default, const char* asrgument values are assumed to have long-lived scope
+// and will not be copied. Use this macro to force a const char* to be copied.
+#define TRACE_STR_COPY(str) node::tracing::TraceStringWithCopy(str)
+
+// By default, uint64 ID argument values are not mangled with the Process ID in
+// TRACE_EVENT_ASYNC macros. Use this macro to force Process ID mangling.
+#define TRACE_ID_MANGLE(id) node::tracing::TraceID::ForceMangle(id)
+
+// By default, pointers are mangled with the Process ID in TRACE_EVENT_ASYNC
+// macros. Use this macro to prevent Process ID mangling.
+#define TRACE_ID_DONT_MANGLE(id) node::tracing::TraceID::DontMangle(id)
+
+// By default, trace IDs are eventually converted to a single 64-bit number. Use
+// this macro to add a scope string.
+#define TRACE_ID_WITH_SCOPE(scope, id) \
+  node::tracing::TraceID::WithScope(scope, id)
+
+// Sets the current sample state to the given category and name (both must be
+// constant strings). These states are intended for a sampling profiler.
+// Implementation note: we store category and name together because we don't
+// want the inconsistency/expense of storing two pointers.
+// |thread_bucket| is [0..2] and is used to statically isolate samples in one
+// thread from others.
+#define TRACE_EVENT_SET_SAMPLING_STATE_FOR_BUCKET(bucket_number, category, \
+                                                  name)                    \
+  node::tracing::TraceEventSamplingStateScope<bucket_number>::Set( \
+      category "\0" name)
+
+// Returns a current sampling state of the given bucket.
+#define TRACE_EVENT_GET_SAMPLING_STATE_FOR_BUCKET(bucket_number) \
+  node::tracing::TraceEventSamplingStateScope<bucket_number>::Current()
+
+// Creates a scope of a sampling state of the given bucket.
+//
+// {  // The sampling state is set within this scope.
+//    TRACE_EVENT_SAMPLING_STATE_SCOPE_FOR_BUCKET(0, "category", "name");
+//    ...;
+// }
+#define TRACE_EVENT_SCOPED_SAMPLING_STATE_FOR_BUCKET(bucket_number, category, \
+                                                     name)                    \
+  node::tracing::TraceEventSamplingStateScope<bucket_number>                   \
+      traceEventSamplingScope(category "\0" name);
+
+
+#define INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE() \
+  *INTERNAL_TRACE_EVENT_UID(category_group_enabled) &                    \
+      (kEnabledForRecording_CategoryGroupEnabledFlags |                  \
+       kEnabledForEventCallback_CategoryGroupEnabledFlags)
+
+// The following macro has no implementation, but it needs to exist since
+// it gets called from scoped trace events. It cannot call UNIMPLEMENTED()
+// since an empty implementation is a valid one.
+#define INTERNAL_TRACE_MEMORY(category, name)
+
+////////////////////////////////////////////////////////////////////////////////
+// Implementation specific tracing API definitions.
+
+// Get a pointer to the enabled state of the given trace category. Only
+// long-lived literal strings should be given as the category group. The
+// returned pointer can be held permanently in a local static for example. If
+// the unsigned char is non-zero, tracing is enabled. If tracing is enabled,
+// TRACE_EVENT_API_ADD_TRACE_EVENT can be called. It's OK if tracing is disabled
+// between the load of the tracing state and the call to
+// TRACE_EVENT_API_ADD_TRACE_EVENT, because this flag only provides an early out
+// for best performance when tracing is disabled.
+// const uint8_t*
+//     TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(const char* category_group)
+#define TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED              \
+  node::tracing::TraceEventHelper::GetCurrentPlatform() \
+      ->GetCategoryGroupEnabled
+
+// Get the number of times traces have been recorded. This is used to implement
+// the TRACE_EVENT_IS_NEW_TRACE facility.
+// unsigned int TRACE_EVENT_API_GET_NUM_TRACES_RECORDED()
+#define TRACE_EVENT_API_GET_NUM_TRACES_RECORDED UNIMPLEMENTED()
+
+// Add a trace event to the platform tracing system.
+// uint64_t TRACE_EVENT_API_ADD_TRACE_EVENT(
+//                    char phase,
+//                    const uint8_t* category_group_enabled,
+//                    const char* name,
+//                    const char* scope,
+//                    uint64_t id,
+//                    uint64_t bind_id,
+//                    int num_args,
+//                    const char** arg_names,
+//                    const uint8_t* arg_types,
+//                    const uint64_t* arg_values,
+//                    unsigned int flags)
+#define TRACE_EVENT_API_ADD_TRACE_EVENT \
+  node::tracing::TraceEventHelper::GetCurrentPlatform()->AddTraceEvent
+
+// Set the duration field of a COMPLETE trace event.
+// void TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
+//     const uint8_t* category_group_enabled,
+//     const char* name,
+//     uint64_t id)
+#define TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION             \
+  node::tracing::TraceEventHelper::GetCurrentPlatform() \
+      ->UpdateTraceEventDuration
+
+// Defines atomic operations used internally by the tracing system.
+#define TRACE_EVENT_API_ATOMIC_WORD intptr_t
+#define TRACE_EVENT_API_ATOMIC_LOAD(var) (var)
+#define TRACE_EVENT_API_ATOMIC_STORE(var, value) (var) = (value)
+
+// The thread buckets for the sampling profiler.
+extern TRACE_EVENT_API_ATOMIC_WORD g_trace_state[3];
+
+#define TRACE_EVENT_API_THREAD_BUCKET(thread_bucket) \
+  g_trace_state[thread_bucket]
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Implementation detail: trace event macros create temporary variables
+// to keep instrumentation overhead low. These macros give each temporary
+// variable a unique name based on the line number to prevent name collisions.
+#define INTERNAL_TRACE_EVENT_UID3(a, b) trace_event_unique_##a##b
+#define INTERNAL_TRACE_EVENT_UID2(a, b) INTERNAL_TRACE_EVENT_UID3(a, b)
+#define INTERNAL_TRACE_EVENT_UID(name_prefix) \
+  INTERNAL_TRACE_EVENT_UID2(name_prefix, __LINE__)
+
+// Implementation detail: internal macro to create static category.
+// No barriers are needed, because this code is designed to operate safely
+// even when the unsigned char* points to garbage data (which may be the case
+// on processors without cache coherency).
+// TODO(fmeawad): This implementation contradicts that we can have a different
+// configuration for each isolate,
+// https://code.google.com/p/v8/issues/detail?id=4563
+#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO_CUSTOM_VARIABLES(             \
+    category_group, atomic, category_group_enabled)                          \
+  category_group_enabled =                                                   \
+      reinterpret_cast<const uint8_t*>(TRACE_EVENT_API_ATOMIC_LOAD(atomic)); \
+  if (!category_group_enabled) {                                             \
+    category_group_enabled =                                                 \
+        TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(category_group);          \
+    TRACE_EVENT_API_ATOMIC_STORE(                                            \
+        atomic, reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD>(               \
+                    category_group_enabled));                                \
+  }
+
+#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group)             \
+  static TRACE_EVENT_API_ATOMIC_WORD INTERNAL_TRACE_EVENT_UID(atomic) = 0; \
+  const uint8_t* INTERNAL_TRACE_EVENT_UID(category_group_enabled);         \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO_CUSTOM_VARIABLES(                 \
+      category_group, INTERNAL_TRACE_EVENT_UID(atomic),                    \
+      INTERNAL_TRACE_EVENT_UID(category_group_enabled));
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD(phase, category_group, name, flags, ...)    \
+  do {                                                                       \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                  \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {  \
+      node::tracing::AddTraceEvent(                                  \
+          phase, INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,     \
+          node::tracing::kGlobalScope, node::tracing::kNoId, \
+          node::tracing::kNoId, flags, ##__VA_ARGS__);               \
+    }                                                                        \
+  } while (0)
+
+// Implementation detail: internal macro to create static category and add begin
+// event if the category is enabled. Also adds the end event when the scope
+// ends.
+#define INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name, ...)           \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                    \
+  node::tracing::ScopedTracer INTERNAL_TRACE_EVENT_UID(tracer);      \
+  if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {    \
+    uint64_t h = node::tracing::AddTraceEvent(                       \
+        TRACE_EVENT_PHASE_COMPLETE,                                          \
+        INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,              \
+        node::tracing::kGlobalScope, node::tracing::kNoId,   \
+        node::tracing::kNoId, TRACE_EVENT_FLAG_NONE, ##__VA_ARGS__); \
+    INTERNAL_TRACE_EVENT_UID(tracer)                                         \
+        .Initialize(INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,  \
+                    h);                                                      \
+  }
+
+#define INTERNAL_TRACE_EVENT_ADD_SCOPED_WITH_FLOW(category_group, name,     \
+                                                  bind_id, flow_flags, ...) \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                   \
+  node::tracing::ScopedTracer INTERNAL_TRACE_EVENT_UID(tracer);     \
+  if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {   \
+    unsigned int trace_event_flags = flow_flags;                            \
+    node::tracing::TraceID trace_event_bind_id(bind_id,             \
+                                                       &trace_event_flags); \
+    uint64_t h = node::tracing::AddTraceEvent(                      \
+        TRACE_EVENT_PHASE_COMPLETE,                                         \
+        INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,             \
+        node::tracing::kGlobalScope, node::tracing::kNoId,  \
+        trace_event_bind_id.raw_id(), trace_event_flags, ##__VA_ARGS__);    \
+    INTERNAL_TRACE_EVENT_UID(tracer)                                        \
+        .Initialize(INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, \
+                    h);                                                     \
+  }
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID(phase, category_group, name, id,      \
+                                         flags, ...)                           \
+  do {                                                                         \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                    \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {    \
+      unsigned int trace_event_flags = flags | TRACE_EVENT_FLAG_HAS_ID;        \
+      node::tracing::TraceID trace_event_trace_id(id,                  \
+                                                          &trace_event_flags); \
+      node::tracing::AddTraceEvent(                                    \
+          phase, INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,       \
+          trace_event_trace_id.scope(), trace_event_trace_id.raw_id(),         \
+          node::tracing::kNoId, trace_event_flags, ##__VA_ARGS__);     \
+    }                                                                          \
+  } while (0)
+
+// Adds a trace event with a given timestamp. Not Implemented.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_TIMESTAMP(phase, category_group, name, \
+                                                timestamp, flags, ...)       \
+  UNIMPLEMENTED()
+
+// Adds a trace event with a given id and timestamp. Not Implemented.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID_AND_TIMESTAMP(     \
+    phase, category_group, name, id, timestamp, flags, ...) \
+  UNIMPLEMENTED()
+
+// Adds a trace event with a given id, thread_id, and timestamp. Not
+// Implemented.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(            \
+    phase, category_group, name, id, thread_id, timestamp, flags, ...) \
+  UNIMPLEMENTED()
+
+// Enter and leave a context based on the current scope.
+#define INTERNAL_TRACE_EVENT_SCOPED_CONTEXT(category_group, name, context) \
+  struct INTERNAL_TRACE_EVENT_UID(ScopedContext) {                         \
+   public:                                                                 \
+    INTERNAL_TRACE_EVENT_UID(ScopedContext)(uint64_t cid) : cid_(cid) {    \
+      TRACE_EVENT_ENTER_CONTEXT(category_group, name, cid_);               \
+    }                                                                      \
+    ~INTERNAL_TRACE_EVENT_UID(ScopedContext)() {                           \
+      TRACE_EVENT_LEAVE_CONTEXT(category_group, name, cid_);               \
+    }                                                                      \
+                                                                           \
+   private:                                                                \
+    /* Local class friendly DISALLOW_COPY_AND_ASSIGN */                    \
+    INTERNAL_TRACE_EVENT_UID(ScopedContext)                                \
+    (const INTERNAL_TRACE_EVENT_UID(ScopedContext)&) {}                    \
+    void operator=(const INTERNAL_TRACE_EVENT_UID(ScopedContext)&) {}      \
+    uint64_t cid_;                                                         \
+  };                                                                       \
+  INTERNAL_TRACE_EVENT_UID(ScopedContext)                                  \
+  INTERNAL_TRACE_EVENT_UID(scoped_context)(context.raw_id());
+
+namespace node {
+namespace tracing {
+
+// Specify these values when the corresponding argument of AddTraceEvent is not
+// used.
+const int kZeroNumArgs = 0;
+const decltype(nullptr) kGlobalScope = nullptr;
+const uint64_t kNoId = 0;
+
+class TraceEventHelper {
+ public:
+  static void SetCurrentPlatform(v8::Platform* platform);
+  static v8::Platform* GetCurrentPlatform();
+};
+
+// TraceID encapsulates an ID that can either be an integer or pointer. Pointers
+// are by default mangled with the Process ID so that they are unlikely to
+// collide when the same pointer is used on different processes.
+class TraceID {
+ public:
+  class WithScope {
+   public:
+    WithScope(const char* scope, uint64_t raw_id)
+        : scope_(scope), raw_id_(raw_id) {}
+    uint64_t raw_id() const { return raw_id_; }
+    const char* scope() const { return scope_; }
+
+   private:
+    const char* scope_ = nullptr;
+    uint64_t raw_id_;
+  };
+
+  class DontMangle {
+   public:
+    explicit DontMangle(const void* raw_id)
+        : raw_id_(static_cast<uint64_t>(reinterpret_cast<uintptr_t>(raw_id))) {}
+    explicit DontMangle(uint64_t raw_id) : raw_id_(raw_id) {}
+    explicit DontMangle(unsigned int raw_id) : raw_id_(raw_id) {}
+    explicit DontMangle(uint16_t raw_id) : raw_id_(raw_id) {}
+    explicit DontMangle(unsigned char raw_id) : raw_id_(raw_id) {}
+    explicit DontMangle(int64_t raw_id)
+        : raw_id_(static_cast<uint64_t>(raw_id)) {}
+    explicit DontMangle(int raw_id) : raw_id_(static_cast<uint64_t>(raw_id)) {}
+    explicit DontMangle(int16_t raw_id)
+        : raw_id_(static_cast<uint64_t>(raw_id)) {}
+    explicit DontMangle(signed char raw_id)
+        : raw_id_(static_cast<uint64_t>(raw_id)) {}
+    explicit DontMangle(WithScope scoped_id)
+        : scope_(scoped_id.scope()), raw_id_(scoped_id.raw_id()) {}
+    const char* scope() const { return scope_; }
+    uint64_t raw_id() const { return raw_id_; }
+
+   private:
+    const char* scope_ = nullptr;
+    uint64_t raw_id_;
+  };
+
+  class ForceMangle {
+   public:
+    explicit ForceMangle(uint64_t raw_id) : raw_id_(raw_id) {}
+    explicit ForceMangle(unsigned int raw_id) : raw_id_(raw_id) {}
+    explicit ForceMangle(uint16_t raw_id) : raw_id_(raw_id) {}
+    explicit ForceMangle(unsigned char raw_id) : raw_id_(raw_id) {}
+    explicit ForceMangle(int64_t raw_id)
+        : raw_id_(static_cast<uint64_t>(raw_id)) {}
+    explicit ForceMangle(int raw_id) : raw_id_(static_cast<uint64_t>(raw_id)) {}
+    explicit ForceMangle(int16_t raw_id)
+        : raw_id_(static_cast<uint64_t>(raw_id)) {}
+    explicit ForceMangle(signed char raw_id)
+        : raw_id_(static_cast<uint64_t>(raw_id)) {}
+    uint64_t raw_id() const { return raw_id_; }
+
+   private:
+    uint64_t raw_id_;
+  };
+
+  TraceID(const void* raw_id, unsigned int* flags)
+      : raw_id_(static_cast<uint64_t>(reinterpret_cast<uintptr_t>(raw_id))) {
+    *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
+  }
+  TraceID(ForceMangle raw_id, unsigned int* flags) : raw_id_(raw_id.raw_id()) {
+    *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
+  }
+  TraceID(DontMangle maybe_scoped_id, unsigned int* flags)
+      : scope_(maybe_scoped_id.scope()), raw_id_(maybe_scoped_id.raw_id()) {}
+  TraceID(uint64_t raw_id, unsigned int* flags) : raw_id_(raw_id) {
+    (void)flags;
+  }
+  TraceID(unsigned int raw_id, unsigned int* flags) : raw_id_(raw_id) {
+    (void)flags;
+  }
+  TraceID(uint16_t raw_id, unsigned int* flags) : raw_id_(raw_id) {
+    (void)flags;
+  }
+  TraceID(unsigned char raw_id, unsigned int* flags) : raw_id_(raw_id) {
+    (void)flags;
+  }
+  TraceID(int64_t raw_id, unsigned int* flags)
+      : raw_id_(static_cast<uint64_t>(raw_id)) {
+    (void)flags;
+  }
+  TraceID(int raw_id, unsigned int* flags)
+      : raw_id_(static_cast<uint64_t>(raw_id)) {
+    (void)flags;
+  }
+  TraceID(int16_t raw_id, unsigned int* flags)
+      : raw_id_(static_cast<uint64_t>(raw_id)) {
+    (void)flags;
+  }
+  TraceID(signed char raw_id, unsigned int* flags)
+      : raw_id_(static_cast<uint64_t>(raw_id)) {
+    (void)flags;
+  }
+  TraceID(WithScope scoped_id, unsigned int* flags)
+      : scope_(scoped_id.scope()), raw_id_(scoped_id.raw_id()) {}
+
+  uint64_t raw_id() const { return raw_id_; }
+  const char* scope() const { return scope_; }
+
+ private:
+  const char* scope_ = nullptr;
+  uint64_t raw_id_;
+};
+
+// Simple union to store various types as uint64_t.
+union TraceValueUnion {
+  bool as_bool;
+  uint64_t as_uint;
+  int64_t as_int;
+  double as_double;
+  const void* as_pointer;
+  const char* as_string;
+};
+
+// Simple container for const char* that should be copied instead of retained.
+class TraceStringWithCopy {
+ public:
+  explicit TraceStringWithCopy(const char* str) : str_(str) {}
+  operator const char*() const { return str_; }
+
+ private:
+  const char* str_;
+};
+
+// Define SetTraceValue for each allowed type. It stores the type and
+// value in the return arguments. This allows this API to avoid declaring any
+// structures so that it is portable to third_party libraries.
+#define INTERNAL_DECLARE_SET_TRACE_VALUE(actual_type, union_member,         \
+                                         value_type_id)                     \
+  static inline void SetTraceValue(actual_type arg, unsigned char* type, \
+                                      uint64_t* value) {                    \
+    TraceValueUnion type_value;                                             \
+    type_value.union_member = arg;                                          \
+    *type = value_type_id;                                                  \
+    *value = type_value.as_uint;                                            \
+  }
+// Simpler form for int types that can be safely casted.
+#define INTERNAL_DECLARE_SET_TRACE_VALUE_INT(actual_type, value_type_id)    \
+  static inline void SetTraceValue(actual_type arg, unsigned char* type, \
+                                      uint64_t* value) {                    \
+    *type = value_type_id;                                                  \
+    *value = static_cast<uint64_t>(arg);                                    \
+  }
+
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(uint64_t, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned int, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(uint16_t, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned char, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int64_t, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int16_t, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(signed char, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE(bool, as_bool, TRACE_VALUE_TYPE_BOOL)
+INTERNAL_DECLARE_SET_TRACE_VALUE(double, as_double, TRACE_VALUE_TYPE_DOUBLE)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const void*, as_pointer,
+                                 TRACE_VALUE_TYPE_POINTER)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const char*, as_string,
+                                 TRACE_VALUE_TYPE_STRING)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const TraceStringWithCopy&, as_string,
+                                 TRACE_VALUE_TYPE_COPY_STRING)
+
+#undef INTERNAL_DECLARE_SET_TRACE_VALUE
+#undef INTERNAL_DECLARE_SET_TRACE_VALUE_INT
+
+// These AddTraceEvent template
+// function is defined here instead of in the macro, because the arg_values
+// could be temporary objects, such as std::string. In order to store
+// pointers to the internal c_str and pass through to the tracing API,
+// the arg_values must live throughout these procedures.
+
+static inline uint64_t AddTraceEvent(char phase,
+                                        const uint8_t* category_group_enabled,
+                                        const char* name, const char* scope,
+                                        uint64_t id, uint64_t bind_id,
+                                        unsigned int flags) {
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(phase, category_group_enabled, name,
+                                         scope, id, bind_id, kZeroNumArgs, NULL,
+                                         NULL, NULL, flags);
+}
+
+template <class ARG1_TYPE>
+static inline uint64_t AddTraceEvent(
+    char phase, const uint8_t* category_group_enabled, const char* name,
+    const char* scope, uint64_t id, uint64_t bind_id, unsigned int flags,
+    const char* arg1_name, const ARG1_TYPE& arg1_val) {
+  const int num_args = 1;
+  uint8_t arg_types[1];
+  uint64_t arg_values[1];
+  SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(
+      phase, category_group_enabled, name, scope, id, bind_id, num_args,
+      &arg1_name, arg_types, arg_values, flags);
+}
+
+template <class ARG1_TYPE, class ARG2_TYPE>
+static inline uint64_t AddTraceEvent(
+    char phase, const uint8_t* category_group_enabled, const char* name,
+    const char* scope, uint64_t id, uint64_t bind_id, unsigned int flags,
+    const char* arg1_name, const ARG1_TYPE& arg1_val, const char* arg2_name,
+    const ARG2_TYPE& arg2_val) {
+  const int num_args = 2;
+  const char* arg_names[2] = {arg1_name, arg2_name};
+  unsigned char arg_types[2];
+  uint64_t arg_values[2];
+  SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
+  SetTraceValue(arg2_val, &arg_types[1], &arg_values[1]);
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(
+      phase, category_group_enabled, name, scope, id, bind_id, num_args,
+      arg_names, arg_types, arg_values, flags);
+}
+
+// Used by TRACE_EVENTx macros. Do not use directly.
+class ScopedTracer {
+ public:
+  // Note: members of data_ intentionally left uninitialized. See Initialize.
+  ScopedTracer() : p_data_(NULL) {}
+
+  ~ScopedTracer() {
+    if (p_data_ && *data_.category_group_enabled)
+      TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
+          data_.category_group_enabled, data_.name, data_.event_handle);
+  }
+
+  void Initialize(const uint8_t* category_group_enabled, const char* name,
+                  uint64_t event_handle) {
+    data_.category_group_enabled = category_group_enabled;
+    data_.name = name;
+    data_.event_handle = event_handle;
+    p_data_ = &data_;
+  }
+
+ private:
+  // This Data struct workaround is to avoid initializing all the members
+  // in Data during construction of this object, since this object is always
+  // constructed, even when tracing is disabled. If the members of Data were
+  // members of this class instead, compiler warnings occur about potential
+  // uninitialized accesses.
+  struct Data {
+    const uint8_t* category_group_enabled;
+    const char* name;
+    uint64_t event_handle;
+  };
+  Data* p_data_;
+  Data data_;
+};
+
+// Used by TRACE_EVENT_BINARY_EFFICIENTx macro. Do not use directly.
+class ScopedTraceBinaryEfficient {
+ public:
+  ScopedTraceBinaryEfficient(const char* category_group, const char* name);
+  ~ScopedTraceBinaryEfficient();
+
+ private:
+  const uint8_t* category_group_enabled_;
+  const char* name_;
+  uint64_t event_handle_;
+};
+
+// TraceEventSamplingStateScope records the current sampling state
+// and sets a new sampling state. When the scope exists, it restores
+// the sampling state having recorded.
+template <size_t BucketNumber>
+class TraceEventSamplingStateScope {
+ public:
+  explicit TraceEventSamplingStateScope(const char* category_and_name) {
+    previous_state_ = TraceEventSamplingStateScope<BucketNumber>::Current();
+    TraceEventSamplingStateScope<BucketNumber>::Set(category_and_name);
+  }
+
+  ~TraceEventSamplingStateScope() {
+    TraceEventSamplingStateScope<BucketNumber>::Set(previous_state_);
+  }
+
+  static inline const char* Current() {
+    return reinterpret_cast<const char*>(
+        TRACE_EVENT_API_ATOMIC_LOAD(g_trace_state[BucketNumber]));
+  }
+
+  static inline void Set(const char* category_and_name) {
+    TRACE_EVENT_API_ATOMIC_STORE(g_trace_state[BucketNumber],
+                                 reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD>(
+                                     const_cast<char*>(category_and_name)));
+  }
+
+ private:
+  const char* previous_state_;
+};
+
+}  // namespace tracing
+}  // namespace node
+
+#endif  // SRC_TRACING_TRACE_EVENT_H_
diff --git a/test/parallel/test-trace-event.js b/test/parallel/test-trace-event.js
new file mode 100644
index 00000000000000..18734705834407
--- /dev/null
+++ b/test/parallel/test-trace-event.js
@@ -0,0 +1,35 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const cp = require('child_process');
+const fs = require('fs');
+
+const CODE = 'for (var i = 0; i < 100000; i++) { "test" + i }';
+const FILE_NAME = 'node_trace.1.log';
+
+common.refreshTmpDir();
+process.chdir(common.tmpDir);
+
+const proc_no_categories = cp.spawn(process.execPath,
+  [ '--trace-events-enabled', '--trace-event-categories', '""', '-e', CODE ]);
+
+proc_no_categories.once('exit', common.mustCall(() => {
+  assert(!common.fileExists(FILE_NAME));
+
+  const proc = cp.spawn(process.execPath,
+  [ '--trace-events-enabled', '-e', CODE ]);
+
+  proc.once('exit', common.mustCall(() => {
+    assert(common.fileExists(FILE_NAME));
+    fs.readFile(FILE_NAME, (err, data) => {
+      const traces = JSON.parse(data.toString()).traceEvents;
+      assert(traces.length > 0);
+      // Values that should be present on all runs to approximate correctness.
+      assert(traces.some((trace) => { return trace.pid === proc.pid; }));
+      assert(traces.some((trace) => { return trace.cat === 'v8'; }));
+      assert(traces.some((trace) => {
+        return trace.name === 'V8.ScriptCompiler';
+      }));
+    });
+  }));
+}));