cc: Make separate interface for BeginFrame ipc from OutputSurface

cc/trees/single_thread_proxy.h

Index: cc/trees/single_thread_proxy.h
diff --git a/cc/trees/single_thread_proxy.h b/cc/trees/single_thread_proxy.h
index ed7b1015a86443011b654e5f994d5700996f6caf..8ec7423929347b8483ea34179a2a2043d8e02d05 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -19,6 +19,7 @@
 
 namespace cc {
 
+class BeginFrameSource;
 class ContextProvider;
 class LayerTreeHost;
 class LayerTreeHostSingleThreadClient;
@@ -30,7 +31,8 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   static scoped_ptr<Proxy> Create(
       LayerTreeHost* layer_tree_host,
       LayerTreeHostSingleThreadClient* client,
-      scoped_refptr<base::SingleThreadTaskRunner> main_task_runner);
+      scoped_refptr<base::SingleThreadTaskRunner> main_task_runner,
+      scoped_ptr<BeginFrameSource> external_begin_frame_source);
   virtual ~SingleThreadProxy();
 
   // Proxy implementation
@@ -59,7 +61,6 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   virtual bool MainFrameWillHappenForTesting() override;
 
   // SchedulerClient implementation
-  virtual BeginFrameSource* ExternalBeginFrameSource() override;
   virtual void WillBeginImplFrame(const BeginFrameArgs& args) override;
   virtual void ScheduledActionSendBeginMainFrame() override;
   virtual DrawResult ScheduledActionDrawAndSwapIfPossible() override;
@@ -117,7 +118,8 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   SingleThreadProxy(
       LayerTreeHost* layer_tree_host,
       LayerTreeHostSingleThreadClient* client,
-      scoped_refptr<base::SingleThreadTaskRunner> main_task_runner);
+      scoped_refptr<base::SingleThreadTaskRunner> main_task_runner,
+      scoped_ptr<BeginFrameSource> external_begin_frame_source);
 
   void BeginMainFrame();
   void BeginMainFrameAbortedOnImplThread();
@@ -162,6 +164,8 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   // This is the callback for the scheduled RequestNewOutputSurface.
   base::CancelableClosure output_surface_creation_callback_;
 
+  scoped_ptr<BeginFrameSource> external_begin_frame_source_;
+
   base::WeakPtrFactory<SingleThreadProxy> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SingleThreadProxy);