Tag some of Mojo heap allocations for the heap profiler.

mojo/public/cpp/bindings/connector.h

Index: mojo/public/cpp/bindings/connector.h
diff --git a/mojo/public/cpp/bindings/connector.h b/mojo/public/cpp/bindings/connector.h
index dcfe8cb930464f41bbc326ffa2d3b2891005b7d4..80ffcd7a60bb2b178a756184b889758a9d2600ad 100644
--- a/mojo/public/cpp/bindings/connector.h
+++ b/mojo/public/cpp/bindings/connector.h
@@ -150,6 +150,8 @@ class MOJO_CPP_BINDINGS_EXPORT Connector
     return task_runner_.get();
   }
 
+  void SetWatcherHeapProfilerTag(const std::string& tag);

[ssid, 2017/01/12 21:52:54]

const char* with a comment saying this must be a const string literal and not
dynamically allocated.

[Jay Civelli, 2017/01/13 01:09:27]

Done.

+
  private:
   // Callback of mojo::Watcher.
   void OnWatcherHandleReady(MojoResult result);
@@ -206,6 +208,9 @@ class MOJO_CPP_BINDINGS_EXPORT Connector
   base::Lock connected_lock_;
   bool connected_ = true;
 
+  // The tag to be used to track heap allocations performed by the watcher.

[Ken Rockot(use gerrit already), 2017/01/12 21:05:22]

nit: Not really allocations performed by the watcher

[Jay Civelli, 2017/01/13 01:09:27]

Clarified.

+  std::string heap_profiler_tag_;

[ssid, 2017/01/12 21:52:54]

Oh this should be const char*.
We do not store the strings in heap profiler so that we don't allocate more
memory for storing category names. It is better if we are tagged with only
strings in the binary. So, const char* everywhere.

[Jay Civelli, 2017/01/13 01:09:27]

Done.

+
   // Create a single weak ptr and use it everywhere, to avoid the malloc/free
   // cost of creating a new weak ptr whenever it is needed.
   // NOTE: This weak pointer is invalidated when the message pipe is closed or