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 e5e976284f8a922c958acab53c161f4133b5f74e..adbd8af8bd7e74be1abaacb5fedc8712c0ccf482 100644
--- a/cc/trees/remote_channel_impl.cc
+++ b/cc/trees/remote_channel_impl.cc
@@ -296,6 +296,10 @@ void RemoteChannelImpl::Stop() {
   main().remote_channel_weak_factory.InvalidateWeakPtrs();
 }
 
+void RemoteChannelImpl::SetMutator(LayerTreeMutator* mutator) {
+  // TODO(vollick): add support for compositor worker.
+}
+
 bool RemoteChannelImpl::SupportsImplScrolling() const {
   return true;
 }