cc: Make separate interface for BeginFrame ipc from OutputSurface

cc/trees/thread_proxy.h

Index: cc/trees/thread_proxy.h
diff --git a/cc/trees/thread_proxy.h b/cc/trees/thread_proxy.h
index 817b36ddae47528caa4a85105e17bcea215a4d9f..641cafabc220e70a9e04bef0dfdc5c49540d6394 100644
--- a/cc/trees/thread_proxy.h
+++ b/cc/trees/thread_proxy.h
@@ -26,6 +26,7 @@ class SingleThreadTaskRunner;
 namespace cc {
 
 class ContextProvider;
+class ExternalBeginFrameSource;
 class InputHandlerClient;
 class LayerTreeHost;
 class ResourceUpdateQueue;
@@ -40,7 +41,8 @@ class CC_EXPORT ThreadProxy : public Proxy,
   static scoped_ptr<Proxy> Create(
       LayerTreeHost* layer_tree_host,
       scoped_refptr<base::SingleThreadTaskRunner> main_task_runner,
-      scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner);
+      scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner,
+      scoped_ptr<ExternalBeginFrameSource> external_begin_frame_source);
 
   virtual ~ThreadProxy();
 
@@ -210,7 +212,6 @@ class CC_EXPORT ThreadProxy : public Proxy,
   virtual void DidManageTiles() override;
 
   // SchedulerClient implementation
-  virtual BeginFrameSource* ExternalBeginFrameSource() override;
   virtual void WillBeginImplFrame(const BeginFrameArgs& args) override;
   virtual void ScheduledActionSendBeginMainFrame() override;
   virtual DrawResult ScheduledActionDrawAndSwapIfPossible() override;
@@ -233,7 +234,8 @@ class CC_EXPORT ThreadProxy : public Proxy,
  protected:
   ThreadProxy(LayerTreeHost* layer_tree_host,
               scoped_refptr<base::SingleThreadTaskRunner> main_task_runner,
-              scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner);
+              scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner,
+              scoped_ptr<ExternalBeginFrameSource> external_begin_frame_source);
 
  private:
   // Called on main thread.
@@ -298,6 +300,8 @@ class CC_EXPORT ThreadProxy : public Proxy,
   base::WeakPtr<ThreadProxy> main_thread_weak_ptr_;
   base::WeakPtr<ThreadProxy> impl_thread_weak_ptr_;
 
+  scoped_ptr<ExternalBeginFrameSource> external_begin_frame_source_;
+
   DISALLOW_COPY_AND_ASSIGN(ThreadProxy);
 };