cc: Introduce BeginFrame sequence numbers and acknowledgements.

content/browser/renderer_host/offscreen_canvas_compositor_frame_sink.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_COMPOSITOR_FRAME_SINK_H_
 #define CONTENT_BROWSER_RENDERER_HOST_OFFSCREEN_CANVAS_COMPOSITOR_FRAME_SINK_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 21 matching lines @@
                              cc::CompositorFrame frame) override;
   void SetNeedsBeginFrame(bool needs_begin_frame) override;
   void AddSurfaceReferences(
       const std::vector<cc::SurfaceReference>& references) override;
   void RemoveSurfaceReferences(
       const std::vector<cc::SurfaceReference>& references) override;
   void EvictFrame() override;
   void Require(const cc::LocalFrameId& local_frame_id,
                const cc::SurfaceSequence& sequence) override;
   void Satisfy(const cc::SurfaceSequence& sequence) override;
+  void BeginFrameDidNotDraw(const cc::BeginFrameAck& ack) override;
 
   // cc::SurfaceFactoryClient implementation.
   void ReturnResources(const cc::ReturnedResourceArray& resources) override;
   void WillDrawSurface(const cc::LocalFrameId& id,
                        const gfx::Rect& damage_rect) override;
   void SetBeginFrameSource(cc::BeginFrameSource* begin_frame_source) override;
 
  private:
   void DidReceiveCompositorFrameAck();
 
   cc::SurfaceId surface_id_;
   std::unique_ptr<cc::SurfaceFactory> surface_factory_;
   cc::mojom::MojoCompositorFrameSinkClientPtr client_;
   int ack_pending_count_ = 0;
   cc::ReturnedResourceArray surface_returned_resources_;
 
   DISALLOW_COPY_AND_ASSIGN(OffscreenCanvasCompositorFrameSink);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_OFFSCREEN_CANVAS_COMPOSITOR_FRAME_SINK_H_