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

cc/trees/remote_channel_impl.cc

Index: cc/trees/remote_channel_impl.cc
diff --git a/cc/trees/remote_channel_impl.cc b/cc/trees/remote_channel_impl.cc
index 0fabdc1d6da8fcbbf1e0ba255d93d0a25aedd686..a71c362129c81435de44baffc94f3d8bf344330d 100644
--- a/cc/trees/remote_channel_impl.cc
+++ b/cc/trees/remote_channel_impl.cc
@@ -297,6 +297,10 @@ void RemoteChannelImpl::Stop() {
   main().remote_channel_weak_factory.InvalidateWeakPtrs();
 }
 
+void RemoteChannelImpl::SetMutator(std::unique_ptr<LayerTreeMutator> mutator) {
+  // TODO(vollick): add support for compositor worker.
+}
+
 bool RemoteChannelImpl::SupportsImplScrolling() const {
   return true;
 }