Add heap allocator usage to task profiler.

base/debug/task_annotator.cc

Index: base/debug/task_annotator.cc
diff --git a/base/debug/task_annotator.cc b/base/debug/task_annotator.cc
index 2747d63c2bf29aa3d356c8c750ff3784b943e66f..97d313af8450671084796db1ee4378743306bc44 100644
--- a/base/debug/task_annotator.cc
+++ b/base/debug/task_annotator.cc
@@ -31,6 +31,7 @@ void TaskAnnotator::RunTask(const char* queue_function,
                             const PendingTask& pending_task) {
   ScopedTaskRunActivity task_activity(pending_task);
 
+  base::debug::HeapUsageTracker heap_usage;

[Primiano Tucci (use gerrit), 2016/10/13 20:47:44]

btw  liked Scoped in the name, made it clear that heap_usage here is a scoped
thing.

[Sigurður Ásgeirsson, 2016/10/14 20:11:35]

Yeah, the problem is that the existing instrumentation collects exclusive
metrics (e.g. an inner measured thing does not contribute cost to the outer
measured thing).
A Scoped* thingy can't support that, as there will always be a gap from
Scoped*::ReadUsage to it passing out of scope, and that gap will be altogether
missing from the tally.

I could reinstate a Scoped* as a subclass of HeapUsageTracker, which only
supports inclusive measurement?

   tracked_objects::TaskStopwatch stopwatch;
   stopwatch.Start();
   tracked_objects::Duration queue_duration =
@@ -54,6 +55,7 @@ void TaskAnnotator::RunTask(const char* queue_function,
   pending_task.task.Run();
 
   stopwatch.Stop();
+

[Primiano Tucci (use gerrit), 2016/10/13 20:47:44]

silly question: what's the point of this scoped HeapUsageTracker if you never
collect the data at the end here?

[Sigurður Ásgeirsson, 2016/10/14 20:11:35]

Good catch - I've moved the HUT into the StopWatch, forgot to clean this up.

   tracked_objects::ThreadData::TallyRunOnNamedThreadIfTracking(
       pending_task, stopwatch);
 }