Add telemetry to track the time an event spent waiting for the main thread.

cc/debug/rendering_stats.h

Index: cc/debug/rendering_stats.h
diff --git a/cc/debug/rendering_stats.h b/cc/debug/rendering_stats.h
index eb01a571b11359baeb7d436bfd9691cd6d49f7fb..dae46c3bc61a1ecffb863e9ccc302962888af70e 100644
--- a/cc/debug/rendering_stats.h
+++ b/cc/debug/rendering_stats.h
@@ -37,6 +37,8 @@ struct CC_EXPORT RenderingStats {
   base::TimeDelta total_deferred_image_decode_time;
   base::TimeDelta total_image_gathering_time;
   base::TimeDelta total_tile_analysis_time;
+  int64 total_impl_thread_to_main_thread_count;

[nduca, 2013/07/08 20:58:32]

these variable names make no sense.

impl_thread_to_main_thread_whats?
total_somethings_sent_from_impl_to_main_thread

or num

same goes for the time...

+  base::TimeDelta total_impl_thread_to_main_thread_time;
   // Note: when adding new members, please remember to update EnumerateFields
   // and Add in rendering_stats.cc.