Add duration estimation data to RenderingStats.

cc/trees/proxy_timing_history.h

 // Copyright 2014 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_TREES_PROXY_TIMING_HISTORY_H_
 #define CC_TREES_PROXY_TIMING_HISTORY_H_
 
 #include "cc/base/rolling_time_delta_history.h"
 
 namespace cc {
 
 class ProxyTimingHistory {
  public:
   ProxyTimingHistory();
   ~ProxyTimingHistory();
 
   base::TimeDelta DrawDurationEstimate() const;
   base::TimeDelta BeginMainFrameToCommitDurationEstimate() const;
   base::TimeDelta CommitToActivateDurationEstimate() const;
 
   void DidBeginMainFrame();
-  void DidCommit();
-  void DidActivatePendingTree();
+  // Returns BeginMainFrame-to-Commit duration.
+  base::TimeDelta DidCommit();
+  // Returns Commit-to-Activate duration.
+  base::TimeDelta DidActivatePendingTree();
   void DidStartDrawing();
   // Returns draw duration.
   base::TimeDelta DidFinishDrawing();
 
  protected:
   RollingTimeDeltaHistory draw_duration_history_;
   RollingTimeDeltaHistory begin_main_frame_to_commit_duration_history_;
   RollingTimeDeltaHistory commit_to_activate_duration_history_;
 
   base::TimeTicks begin_main_frame_sent_time_;
   base::TimeTicks commit_complete_time_;
   base::TimeTicks start_draw_time_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROXY_TIMING_HISTORY_H_