Reland of [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..e70185d1ba3add70a0419f71c88bb84fbfebc023 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);
+  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 cluster allocations.
+  std::vector<const char*> task_contexts_;
+
   DISALLOW_COPY_AND_ASSIGN(AllocationContextTracker);
 };