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

cc/debug/rendering_stats.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_DEBUG_RENDERING_STATS_H_
 #define CC_DEBUG_RENDERING_STATS_H_
 
 #include "base/basictypes.h"
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
@@ skipping 19 matching lines @@
   int64 num_layers_drawn;
   int64 num_missing_tiles;
   int64 total_deferred_image_decode_count;
   int64 total_deferred_image_cache_hit_count;
   int64 total_image_gathering_count;
   int64 total_tiles_analyzed;
   int64 solid_color_tiles_analyzed;
   base::TimeDelta total_deferred_image_decode_time;
   base::TimeDelta total_image_gathering_time;
   base::TimeDelta total_tile_analysis_time;
+  base::TimeDelta average_impl_thread_to_main_thread_time;
   // Note: when adding new members, please remember to update EnumerateFields
   // and Add in rendering_stats.cc.
 
   RenderingStats();
 
   // In conjunction with EnumerateFields, this allows the embedder to
   // enumerate the values in this structure without
   // having to embed references to its specific member variables. This
   // simplifies the addition of new fields to this type.
   class Enumerator {
@@ skipping 11 matching lines @@
   // Outputs the fields in this structure to the provided enumerator.
   void EnumerateFields(Enumerator* enumerator) const;
 
   // Add fields of |other| to the fields in this structure.
   void Add(const RenderingStats& other);
 };
 
 }  // namespace cc
 
 #endif  // CC_DEBUG_RENDERING_STATS_H_