cc: Make separate interface for BeginFrame ipc from OutputSurface

cc/layers/texture_layer_unittest.cc

Index: cc/layers/texture_layer_unittest.cc
diff --git a/cc/layers/texture_layer_unittest.cc b/cc/layers/texture_layer_unittest.cc
index 8846152f67aaf521187df8a82cd0a322d646e582..b1152db0d0f934f895c44087f3885bf2f7eebd55 100644
--- a/cc/layers/texture_layer_unittest.cc
+++ b/cc/layers/texture_layer_unittest.cc
@@ -52,7 +52,9 @@ class MockLayerTreeHost : public LayerTreeHost {
  public:
   explicit MockLayerTreeHost(FakeLayerTreeHostClient* client)
       : LayerTreeHost(client, NULL, LayerTreeSettings()) {
-    InitializeSingleThreaded(client, base::MessageLoopProxy::current());
+    InitializeSingleThreaded(client,
+                             base::MessageLoopProxy::current(),
+                             scoped_ptr<ExternalBeginFrameSource>());
   }
 
   MOCK_METHOD0(SetNeedsCommit, void());