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

content/renderer/gpu/render_widget_compositor.h

 // Copyright (c) 2013 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_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 #define CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 93 matching lines @@
       const std::string& name,
       std::unique_ptr<base::Value> value,
       const base::Callback<void(std::unique_ptr<base::Value>)>& callback);
   bool SendMessageToMicroBenchmark(int id, std::unique_ptr<base::Value> value);
   void SetFrameSinkId(const cc::FrameSinkId& frame_sink_id);
   void OnHandleCompositorProto(const std::vector<uint8_t>& proto);
   void SetPaintedDeviceScaleFactor(float device_scale);
   void SetDeviceColorSpace(const gfx::ColorSpace& color_space);
 
   // WebLayerTreeView implementation.
+  cc::FrameSinkId getFrameSinkId() override;

[Fady Samuel, 2017/01/19 04:05:43]

Return a const cc::FrameSinkId& instead?

[xlai (Olivia), 2017/01/19 16:43:56]

Can't do that. This function is overriding another virtual function in
WebLayerTreeView, which must be creating an empty FrameSinkId in its
implementation.

   void setRootLayer(const blink::WebLayer& layer) override;
   void clearRootLayer() override;
   cc::AnimationHost* compositorAnimationHost() override;
   void setViewportSize(const blink::WebSize& device_viewport_size) override;
   blink::WebSize getViewportSize() const override;
   virtual blink::WebFloatPoint adjustEventPointForPinchZoom(
       const blink::WebFloatPoint& point) const;
   void setDeviceScaleFactor(float device_scale) override;
   void setBackgroundColor(blink::WebColor color) override;
   void setHasTransparentBackground(bool transparent) override;
@@ skipping 110 matching lines @@
   RemoteProtoChannel::ProtoReceiver* remote_proto_channel_receiver_;
 
   cc::FrameSinkId frame_sink_id_;
 
   base::WeakPtrFactory<RenderWidgetCompositor> weak_factory_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_