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 eaca0dae3b75a916ccc1f4f09295e1e111d6c805..e2a0d8d1f16e356857654141fc383313e813374f 100644
--- a/cc/trees/remote_channel_main.cc
+++ b/cc/trees/remote_channel_main.cc
@@ -68,6 +68,12 @@ void RemoteChannelMain::InitializeOutputSurfaceOnImpl(
   NOTREACHED() << "Should not be called on the server LayerTreeHost";
 }
 
+void RemoteChannelMain::InitializeMutatorOnImpl(
+    std::unique_ptr<LayerTreeMutator> mutator) {
+  // TODO(vollick): add support for CompositorWorker.
+  NOTIMPLEMENTED();
+}
+
 void RemoteChannelMain::MainThreadHasStoppedFlingingOnImpl() {
   proto::CompositorMessage proto;
   proto::CompositorMessageToImpl* to_impl_proto = proto.mutable_to_impl();