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 89378f5717cdead1535241acab8d3276d7870df3..7eb000a5eefed63fbe42efc65ff59f21aae269d4 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);
   ~SingleThreadProxy() override;
 
   // Proxy implementation
@@ -59,7 +61,6 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   bool MainFrameWillHappenForTesting() override;
 
   // SchedulerClient implementation
-  BeginFrameSource* ExternalBeginFrameSource() override;
   void WillBeginImplFrame(const BeginFrameArgs& args) override;
   void ScheduledActionSendBeginMainFrame() override;
   DrawResult ScheduledActionDrawAndSwapIfPossible() override;
@@ -114,7 +115,8 @@ 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();
@@ -159,6 +161,8 @@ 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);