Read compositor VSync information from platform, when possible

ui/compositor/compositor.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_COMPOSITOR_COMPOSITOR_H_
 #define UI_COMPOSITOR_COMPOSITOR_H_
 
 #include <string>
 
 #include "base/containers/hash_tables.h"
@@ skipping 235 matching lines @@
 
   // Signals swap has been posted.
   void OnSwapBuffersPosted();
 
   // Signals swap has completed.
   void OnSwapBuffersComplete();
 
   // 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 {}
   virtual void DidBeginMainFrame() OVERRIDE {}
   virtual void Animate(double frame_begin_time) OVERRIDE {}
   virtual void Layout() OVERRIDE;
   virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
                                    float page_scale) OVERRIDE {}
   virtual scoped_ptr<cc::OutputSurface> CreateOutputSurface(bool fallback)
       OVERRIDE;
@@ skipping 50 matching lines @@
   // layers on.
   float device_scale_factor_;
 
   int last_started_frame_;
   int last_ended_frame_;
 
   bool next_draw_is_resize_;
 
   bool disable_schedule_composite_;
 
+  base::TimeDelta authoritative_vsync_interval_;
+
   CompositorLock* compositor_lock_;
 
   // Prevent more than one draw from being scheduled.
   bool defer_draw_scheduling_;
 
   // Used to prevent Draw()s while a composite is in progress.
   bool waiting_on_compositing_end_;
   bool draw_on_compositing_end_;
 
   base::WeakPtrFactory<Compositor> schedule_draw_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Compositor);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_COMPOSITOR_H_