cc: Measure compositor timing with finer granularity

cc/trees/single_thread_proxy.h

Index: cc/trees/single_thread_proxy.h
diff --git a/cc/trees/single_thread_proxy.h b/cc/trees/single_thread_proxy.h
index da807dced5101a4cd7a0fed4b170100258cfef72..8bec2b133f991fee23278c337f6ca12462eb7add 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -101,6 +101,7 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   void PostDelayedAnimationTaskOnImplThread(const base::Closure& task,
                                             base::TimeDelta delay) override {}
   void DidActivateSyncTree() override;
+  void WillPrepareTiles() override;
   void DidPrepareTiles() override;
   void DidCompletePageScaleAnimationOnImplThread() override;
   void OnDrawForOutputSurface() override;