Refactor external begin frame source into a base class

content/renderer/gpu/compositor_external_begin_frame_source.h

Index: content/renderer/gpu/compositor_external_begin_frame_source.h
diff --git a/content/renderer/gpu/compositor_external_begin_frame_source.h b/content/renderer/gpu/compositor_external_begin_frame_source.h
index 8a965772f36ddd4493fa854e7e66ba116c60aa36..64aa7d51944f70c99db4e8fb859c685a2b8a12a3 100644
--- a/content/renderer/gpu/compositor_external_begin_frame_source.h
+++ b/content/renderer/gpu/compositor_external_begin_frame_source.h
@@ -22,8 +22,15 @@ 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(
@@ -38,6 +45,9 @@ class CompositorExternalBeginFrameSource
   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<
@@ -62,22 +72,20 @@ class CompositorExternalBeginFrameSource
     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);
 };