[cc] Track observer status in ExternalBeginFrameSource.

components/exo/compositor_frame_sink_holder.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 COMPONENTS_EXO_COMPOSITOR_FRAME_SINK_HOLDER_H_
 #define COMPONENTS_EXO_COMPOSITOR_FRAME_SINK_HOLDER_H_
 
 #include <list>
 #include <map>
 #include <memory>
@@ skipping 44 matching lines @@
   void OnBeginFrame(const cc::BeginFrameArgs& args) override;
   void ReclaimResources(const cc::ReturnedResourceArray& resources) override;
   void WillDrawSurface() override;
 
   // Overridden from cc::BeginFrameObserver:
   const cc::BeginFrameArgs& LastUsedBeginFrameArgs() const override;
   void OnBeginFrameSourcePausedChanged(bool paused) override;
 
   // Overridden from cc::ExternalBeginFrameSouceClient:
   void OnNeedsBeginFrames(bool needs_begin_frames) override;
+  void OnDidFinishFrame(const cc::BeginFrameAck& ack) override;
 
   // Overridden from SurfaceObserver:
   void OnSurfaceDestroying(Surface* surface) override;
 
  private:
   friend class base::RefCounted<CompositorFrameSinkHolder>;
 
   ~CompositorFrameSinkHolder() override;
 
   void UpdateNeedsBeginFrame();
@@ skipping 10 matching lines @@
   cc::BeginFrameArgs last_begin_frame_args_;
 
   base::WeakPtrFactory<CompositorFrameSinkHolder> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CompositorFrameSinkHolder);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_COMPOSITOR_FRAME_SINK_HOLDER_H_