Tracking bug for re-establishing breakpoints in debuggers

[elliette]

Spinning this off of dart-lang/webdev#2257, although this issue involves work for other systems besides DevTools. But I would like everything to be tracked in one place.

This all began because on web we were experiencing an issue of "phantom breakpoints" where a breakpoint that a user had removed was still being hit in Chrome, see dart-lang/webdev#2257. We would like to remove that behavior and have the debugging clients be the source of truth for breakpoints. However, while DAP clients re-establish breakpoints on hot-restart, DevTools does not.

On further investigation, we discovered that breakpoints set along the app's initial startup path in DevTools and in DAP clients don't always get hit on hot-restart or (for web) when users refresh the page. This is because breakpoints are re-set by the debugging client after the app's isolate has already started. Therefore, we want to use a combination of:

• set_isolates_paused_on_start - make sure the app initially starts out paused
• requirePermissionToResume(onPauseStart: true) - make sure that all connected debugging clients using set_isolates_paused_on_start send resume event before resuming
• debugging clients send resume after they have set breakpoints

Therefore, the work required here:

Note: the following needs to be done before rolling unpinning DWDS and rolling it into google3. It was pinned here: dart-lang/sdk@4642c73

In DWDS:

• Remove the logic to re-establish breakpoints after a hot-restart from DWDS (DONE: Do not persist breakpoints across hot restarts or page refreshes dart-lang/webdev#2371)
• DWDS needs to implement the VM Service setFlag method for pause_isolates_on_start (DONE: Implement setFlag for 'pause_isolates_on_start' dart-lang/webdev#2373)
• During hot-restart, wait to run main if pause-isolates-on-start is true (DONE: During hot-restart, wait to run main when pause_isolates_on_start is true dart-lang/webdev#2378)
• After the debugger disconnects, ensure that we no longer pause for hot-restarts/page reloads (DONE: Fix reading pause_isolates_on_start value from the DWDS dart-lang/webdev#2398)
• Follow-up: Make pauseIsolatesOnStart optional (DONE: Make pauseIsolatesOnStart an optional parameter to hot-restart dart-lang/webdev#2397)
• Follow-up: Send a kPausePostRequest event after restarting to notify clients to resume (DONE: Send a kPausePostRequest after restarting to notify clients to resume dart-lang/webdev#2441)
• Follow-up: Implement the getFlagList API (DONE: Implement the VM service getFlagList API dart-lang/webdev#2438)

In DevTools:

• Add logic to re-establish breakpoints after a hot-restart to DevTools (DONE: Re-establish breakpoints on hot-restart  #7205)
• Call setFlag('pause_isolates_on_start') and requirePermissionToResume(onPauseStart: true), then only resume once breakpoints are set (DONE: Configure DevTools to pause isolates on hot restart, and then only resume once breakpoints have been set #7234)

In DDS:

• Add requireUserPermissionToResume and readyToResume (DONE BY @bkonyi): dart-lang/sdk@5536951)
• Determine initial requireUserPermissionToResume values from the VM service flags (DONE: dart-lang/sdk@9382e58)

Note: This can be done after rolling DWDS into google3

In Flutter Engine:

• [ ] Make sure pause_isolates_on_start is respected (see Setting flag pause_isolates_on_start does not pause isolates on hot-restart  dart-lang/sdk#54900, currently flutter_engine isn't respecting the flag so setting it in the VM Service doesn't do anything)

In DAP:

• Set requirePermissionToResume and requireUserPermissionToResume for onPauseStart and onPauseExit so that DDS waits for DAP's permission before resuming the isolate (DONE: dart-lang/sdk@93556ae)

Make sure pause_isolates_on_start is respected for hot-restarts and page refreshes for web (changes required in multiple locations):

• Page refresh when running from flutter_tools (DONE:: Wait for a resume event to run the main() method after a page refresh dart-lang/webdev#2431)
• hot-restart when running from flutter_tools (DONE: During hot-restart, wait to run main when pause_isolates_on_start is true dart-lang/webdev#2378)
• Hot-restart and page-refreshes in g3: (DONE: b/335227246)
• Mirror of hot-restart in g3 (DONE: https://dart-review.googlesource.com/c/sdk/+/355880)

[elliette]

Since this requires coordination across multiple debugging clients, it makes sense to pin DWDS in g3 until everything is ready to land.