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 da8cc26478658f8c1edebaae03af37e875c733ec..ec7b2adb1687515dda3d6a6eca017b9eade3d3bd 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;