[cc] Add and use BeginFrameAck for DidFinishFrame.

content/renderer/gpu/compositor_external_begin_frame_source.h

 // Copyright 2014 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_COMPOSITOR_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 #define CONTENT_RENDERER_GPU_COMPOSITOR_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 
 #include <unordered_set>
 
 #include "base/compiler_specific.h"
@@ skipping 25 matching lines @@
   explicit CompositorExternalBeginFrameSource(
       CompositorForwardingMessageFilter* filter,
       IPC::SyncMessageFilter* sync_message_filter,
       int routing_id);
   ~CompositorExternalBeginFrameSource() override;
 
   // cc::BeginFrameSource implementation.
   void AddObserver(cc::BeginFrameObserver* obs) override;
   void RemoveObserver(cc::BeginFrameObserver* obs) override;
   void DidFinishFrame(cc::BeginFrameObserver* obs,
-                      size_t remaining_frames) override {}
+                      const cc::BeginFrameAck& ack) override {}

[brianderson, 2016/12/21 20:15:06]

Are you planning to implement this in a followup patch?

[Eric Seckler, 2016/12/22 11:11:48]

Yup, together with ack-tracking within ExternalBFS. Added a TODO.

   bool IsThrottled() const override;
 
   // cc::ExternalBeginFrameSourceClient implementation.
   void OnNeedsBeginFrames(bool need_begin_frames) override;
 
  private:
   class CompositorExternalBeginFrameSourceProxy
       : public base::RefCountedThreadSafe<
                    CompositorExternalBeginFrameSourceProxy> {
    public:
@@ skipping 30 matching lines @@
   scoped_refptr<IPC::SyncMessageFilter> message_sender_;
   int routing_id_;
   CompositorForwardingMessageFilter::Handler begin_frame_source_filter_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(CompositorExternalBeginFrameSource);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_COMPOSITOR_EXTERNAL_BEGIN_FRAME_SOURCE_H_