Make OffscreenCanvas animation in sync with its placeholder canvas's parent frame rate

content/browser/renderer_host/offscreen_canvas_surface_manager.h

 // Copyright 2016 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 CONTENT_BROWSER_RENDERER_HOST_OFFSCREEN_CANVAS_SURFACE_MANAGER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_OFFSCREEN_CANVAS_SURFACE_MANAGER_H_
 
 #include "base/memory/weak_ptr.h"
 #include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surface_observer.h"
 #include "content/browser/renderer_host/offscreen_canvas_surface_impl.h"
 
 namespace content {
 
 class CONTENT_EXPORT OffscreenCanvasSurfaceManager
     : public cc::SurfaceObserver {
  public:
   OffscreenCanvasSurfaceManager();
   virtual ~OffscreenCanvasSurfaceManager();
 
   static OffscreenCanvasSurfaceManager* GetInstance();
 
+  // Registration of the frame sink with the given frame sink id to its parent
+  // frame sink (if it has one), so that parent frame is able to send signals
+  // to it on begin frame.
+  void RegisterFrameSinkToItsParent(cc::FrameSinkId);
+  void UnregisterFrameSinkFromItsParent(cc::FrameSinkId);
+
   void RegisterOffscreenCanvasSurfaceInstance(cc::FrameSinkId,
                                               OffscreenCanvasSurfaceImpl*);
   void UnregisterOffscreenCanvasSurfaceInstance(cc::FrameSinkId);
   OffscreenCanvasSurfaceImpl* GetSurfaceInstance(cc::FrameSinkId);
 
  private:
   friend class OffscreenCanvasSurfaceManagerTest;
 
   // cc::SurfaceObserver implementation.
   void OnSurfaceCreated(const cc::SurfaceInfo& surface_info) override;
   void OnSurfaceDamaged(const cc::SurfaceId&, bool* changed) override {}
 
   // When an OffscreenCanvasSurfaceImpl instance is destructed, it will
   // unregister the corresponding entry from this map.
   std::unordered_map<cc::FrameSinkId,
                      OffscreenCanvasSurfaceImpl*,
                      cc::FrameSinkIdHash>
       registered_surface_instances_;
   DISALLOW_COPY_AND_ASSIGN(OffscreenCanvasSurfaceManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_OFFSCREEN_CANVAS_SURFACE_MANAGER_H_