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 4beb9fffcbdfe9f88a14b6410ca36f3b87ecc949..a3af54b04f22010e1a6f38713f281356fd161312 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -290,8 +290,11 @@ 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 {}
@@ -362,6 +365,8 @@ class COMPOSITOR_EXPORT Compositor
 
   bool disable_schedule_composite_;
 
+  base::TimeDelta authoritative_vsync_interval_;
+
   CompositorLock* compositor_lock_;
 
   // Prevent more than one draw from being scheduled.