[tracing] Adding task information to heap profiler

base/trace_event/heap_profiler_allocation_context_tracker.h

Index: base/trace_event/heap_profiler_allocation_context_tracker.h
diff --git a/base/trace_event/heap_profiler_allocation_context_tracker.h b/base/trace_event/heap_profiler_allocation_context_tracker.h
index 5d32c64952266475fcb440476febf208f618a39f..28e2cc9ca934b5c0bddf77c9f99727cbd094252e 100644
--- a/base/trace_event/heap_profiler_allocation_context_tracker.h
+++ b/base/trace_event/heap_profiler_allocation_context_tracker.h
@@ -58,6 +58,11 @@ class BASE_EXPORT AllocationContextTracker {
   // Pops a frame from the thread-local pseudo stack.
   void PopPseudoStackFrame(StackFrame frame);
 
+  // Push and pop current task's context. A stack is used to support nested
+  // tasks and the top of the stack will be used in allocation context.
+  void PushCurrentTaskContext(const char* context);

[Primiano Tucci (use gerrit), 2016/03/31 15:37:16]

I aware about the fact that I am a real pain on naming.
Since this is either a task name or file path (don't remember which ATM) why
don't we make it explicit?
"context" makes it cryptic to understand what it really is.
It's a string, should be straightforward to tell what the content of such string
is when looking at the code.

[ssid, 2016/03/31 16:02:49]

Yes but I feel this will be reused for some other reason very soon. That time
there will not be a need to rename it. For example if we want to add IPC names
as context instead of stack frame, or even add the posted function name instead
of file name, this can still be used. I could also add context like WebKit or
skia. Do you strongly prefer that I change it to task_posted_file_name?

[Primiano Tucci (use gerrit), 2016/03/31 16:10:59]

Ahh ok, if you have upcoming use cases in mind it's ok leaving it as it is (but
then you have to figure out something below in the logic that strips the paths)

[ssid, 2016/04/01 04:34:54]

I changed the comment and function name. wdyt?

[Primiano Tucci (use gerrit), 2016/04/01 08:36:16]

Much better, thanks.

+  void PopCurrentTaskContext(const char* context);
+
   // Returns a snapshot of the current thread-local context.
   AllocationContext GetContextSnapshot();
 
@@ -74,6 +79,10 @@ class BASE_EXPORT AllocationContextTracker {
   // The thread name is used as the first entry in the pseudo stack.
   const char* thread_name_;
 
+  // Stack of tasks' contexts. Context serves as a different dimension than
+  // pseudo stack to study the heap.

[Primiano Tucci (use gerrit), 2016/03/31 15:37:16]

s/to study the heap/to cluster allocations/

[ssid, 2016/04/01 04:34:54]

Done.

+  std::vector<const char*> task_contexts_;
+
   DISALLOW_COPY_AND_ASSIGN(AllocationContextTracker);
 };