Add duration estimation data to RenderingStats.

cc/trees/proxy_timing_history.cc

Index: cc/trees/proxy_timing_history.cc
diff --git a/cc/trees/proxy_timing_history.cc b/cc/trees/proxy_timing_history.cc
index e920f285697911cd449f96d05973015359d45928..c3f254d7fc4aaa85cd62512fc73011b5dce69dcb 100644
--- a/cc/trees/proxy_timing_history.cc
+++ b/cc/trees/proxy_timing_history.cc
@@ -41,15 +41,21 @@ void ProxyTimingHistory::DidBeginMainFrame() {
   begin_main_frame_sent_time_ = base::TimeTicks::HighResNow();
 }
 
-void ProxyTimingHistory::DidCommit() {
+base::TimeDelta ProxyTimingHistory::DidCommit() {
   commit_complete_time_ = base::TimeTicks::HighResNow();
+  base::TimeDelta begin_main_frame_to_commit_duration =
+      commit_complete_time_ - begin_main_frame_sent_time_;
   begin_main_frame_to_commit_duration_history_.InsertSample(
-      commit_complete_time_ - begin_main_frame_sent_time_);
+      begin_main_frame_to_commit_duration);
+  return begin_main_frame_to_commit_duration;
 }
 
-void ProxyTimingHistory::DidActivatePendingTree() {
+base::TimeDelta ProxyTimingHistory::DidActivatePendingTree() {
+  base::TimeDelta commit_to_activate_duration =
+      base::TimeTicks::HighResNow() - commit_complete_time_;
   commit_to_activate_duration_history_.InsertSample(
-      base::TimeTicks::HighResNow() - commit_complete_time_);
+      commit_to_activate_duration);
+  return commit_to_activate_duration;
 }
 
 void ProxyTimingHistory::DidStartDrawing() {