compositor-worker: Initialize CW machinery plumbing to compositor and fire CW rAF callbacks.

cc/trees/remote_channel_main.cc

Index: cc/trees/remote_channel_main.cc
diff --git a/cc/trees/remote_channel_main.cc b/cc/trees/remote_channel_main.cc
index 015692810ea7b4bf0700e6255e278e6b6ab1f6d7..90c514691d118236cd6abc67e3456b9e18a0dcc4 100644
--- a/cc/trees/remote_channel_main.cc
+++ b/cc/trees/remote_channel_main.cc
@@ -65,6 +65,10 @@ void RemoteChannelMain::InitializeOutputSurfaceOnImpl(
   NOTREACHED() << "Should not be called on the server LayerTreeHost";
 }
 
+void RemoteChannelMain::InitializeMutatorOnImpl(LayerTreeMutator* mutator) {
+  // TODO(vollick): add support for CompositorWorker.
+}
+
 void RemoteChannelMain::MainThreadHasStoppedFlingingOnImpl() {
   proto::CompositorMessage proto;
   proto::CompositorMessageToImpl* to_impl_proto = proto.mutable_to_impl();