Read compositor VSync information from platform, when possible

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index 88bf42182238aac3729e9ce40115ff668242836c..62bee49e1e6734c2033c160511e81fa476ceb3ca 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -244,8 +244,11 @@ class COMPOSITOR_EXPORT Compositor
   // Signals swap has aborted (e.g. lost context).
   void OnSwapBuffersAborted();
 
+  // If |interval_is_authoritative| is true, then |interval| is used as the
+  // authoritative vsync interval for future calls to OnUpdateVSyncParameters().
   void OnUpdateVSyncParameters(base::TimeTicks timebase,
-                               base::TimeDelta interval);
+                               base::TimeDelta interval,
+                               bool interval_is_authoritative);
 
   // LayerTreeHostClient implementation.
   virtual void WillBeginMainFrame(int frame_id) OVERRIDE {}
@@ -316,6 +319,8 @@ class COMPOSITOR_EXPORT Compositor
 
   bool disable_schedule_composite_;
 
+  base::TimeDelta authoritative_vsync_interval_;
+
   CompositorLock* compositor_lock_;
 
   // Prevent more than one draw from being scheduled.