Refactor external begin frame source into a base class

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"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "cc/scheduler/begin_frame_source.h"
 #include "content/renderer/gpu/compositor_forwarding_message_filter.h"
 
 namespace IPC {
 class Message;
 class SyncMessageFilter;
 }
 
 namespace content {
 
 // This class can be created only on the main thread, but then becomes pinned
 // to a fixed thread where cc::Scheduler is running.
+//
+// TODO(enne): This only implements the BeginFrameSource interface to
+// make it easier to give to cc as an external begin frame source.  In the
+// future, if this is owned by an output surface, then the internal
+// cc::ExternalBeginFrameSource can be the BeginFrameSource passed to cc
+// directly rather than proxied by this class.
 class CompositorExternalBeginFrameSource
     : public cc::BeginFrameSource,
+      public cc::ExternalBeginFrameSourceClient,
       public NON_EXPORTED_BASE(base::NonThreadSafe) {
  public:
   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 {}
 
+  // cc::ExternalBeginFrameSourceClient implementation.
+  void OnNeedsBeginFrames(bool need_begin_frames) override;
+
  private:
   class CompositorExternalBeginFrameSourceProxy
       : public base::RefCountedThreadSafe<
                    CompositorExternalBeginFrameSourceProxy> {
    public:
     explicit CompositorExternalBeginFrameSourceProxy(
         CompositorExternalBeginFrameSource* begin_frame_source)
         : begin_frame_source_(begin_frame_source) {}
     void ClearBeginFrameSource() { begin_frame_source_ = NULL; }
     void OnMessageReceived(const IPC::Message& message) {
       if (begin_frame_source_)
         begin_frame_source_->OnMessageReceived(message);
     }
 
    private:
     friend class base::RefCountedThreadSafe<
                      CompositorExternalBeginFrameSourceProxy>;
     virtual ~CompositorExternalBeginFrameSourceProxy() {}
 
     CompositorExternalBeginFrameSource* begin_frame_source_;
 
     DISALLOW_COPY_AND_ASSIGN(CompositorExternalBeginFrameSourceProxy);
   };
 
-  void SetClientReady();
   void OnMessageReceived(const IPC::Message& message);
-
   void OnSetBeginFrameSourcePaused(bool paused);
   void OnBeginFrame(const cc::BeginFrameArgs& args);
   bool Send(IPC::Message* message);
 
+  // Shared helper implementation.
+  cc::ExternalBeginFrameSource external_begin_frame_source_;
+
   scoped_refptr<CompositorForwardingMessageFilter> begin_frame_source_filter_;
   scoped_refptr<CompositorExternalBeginFrameSourceProxy>
       begin_frame_source_proxy_;
   scoped_refptr<IPC::SyncMessageFilter> message_sender_;
   int routing_id_;
   CompositorForwardingMessageFilter::Handler begin_frame_source_filter_handler_;
-  cc::BeginFrameArgs missed_begin_frame_args_;
-  std::unordered_set<cc::BeginFrameObserver*> observers_;
-  bool paused_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(CompositorExternalBeginFrameSource);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_COMPOSITOR_EXTERNAL_BEGIN_FRAME_SOURCE_H_