profiler: fix goroutineswait profile frame order (#850)

The frames were showing up in reverse in the UI. Not sure why I wrote
the code to prepend instead of append the frames, but it's wrong and
this patch fixes it.

Fixes PROF-2908

profiler/profile.go

@@ -327,7 +327,7 @@ func goroutineDebug2ToPprof(r io.Reader, w io.Writer, t time.Time) (err error) {
 			p.Location = append(p.Location, location)
 			locationID++
 
-			sample.Location = append([]*pprofile.Location{location}, sample.Location...)
+			sample.Location = append(sample.Location, location)
 		}
 
 		p.Sample = append(p.Sample, sample)

profiler/profile_test.go

@@ -129,6 +129,15 @@ main.main()
 		// pro tip: enable line below to inspect the pprof output using cli tools
 		// ioutil.WriteFile(prof.name, prof.data, 0644)
 
+		requireFunctions := func(t *testing.T, s *pprofile.Sample, want []string) {
+			t.Helper()
+			var got []string
+			for _, loc := range s.Location {
+				got = append(got, loc.Line[0].Function.Name)
+			}
+			require.Equal(t, want, got)
+		}
+
 		pp, err := pprofile.Parse(bytes.NewReader(prof.data))
 		require.NoError(t, err)
 		// timestamp
@@ -146,9 +155,16 @@ main.main()
 		require.Equal(t, []int64{3}, pp.Sample[1].NumLabel["goid"])
 		require.Equal(t, []string{"id"}, pp.Sample[1].NumUnit["goid"])
 		// Virtual frame for "frames elided" goroutine
-		require.Equal(t, 3, len(pp.Sample[2].Location))
+		requireFunctions(t, pp.Sample[2], []string{
+			"main.stackDump",
+			"main.main",
+			"...additional frames elided...",
+		})
 		// Virtual frame go "created by" frame
-		require.Equal(t, 2, len(pp.Sample[1].Location))
+		requireFunctions(t, pp.Sample[1], []string{
+			"time.Sleep",
+			"main.indirectShortSleepLoop2",
+		})
 	})
 }