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 42d943d32a7c1047f76abfe20e1e728e86de1476..2150359897abd1548c94254a5ac45e56e95d4469 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;
 }