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 030f1ca9b708698e0dd6b7af07fa65fd9b2ff69e..2f3510e1bb6022f0040198caa0ded8c7a78ea569 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -19,6 +19,7 @@
 namespace cc {
 
 class ContextProvider;
+class ExternalBeginFrameSource;
 class LayerTreeHost;
 class LayerTreeHostSingleThreadClient;
 
@@ -29,7 +30,8 @@ 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<ExternalBeginFrameSource> external_begin_frame_source);
   virtual ~SingleThreadProxy();
 
   // Proxy implementation
@@ -58,7 +60,6 @@ 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;
@@ -116,7 +117,8 @@ 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<ExternalBeginFrameSource> external_begin_frame_source);
 
   void BeginMainFrame();
   void BeginMainFrameAbortedOnImplThread();
@@ -153,6 +155,8 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   bool commit_was_deferred_;
   bool commit_requested_;
 
+  scoped_ptr<ExternalBeginFrameSource> external_begin_frame_source_;
+
   base::WeakPtrFactory<SingleThreadProxy> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SingleThreadProxy);