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 a231bcbe061dde24317cbce8969b914dde928e2f..1bf79d6094aa83223f91ba77bb033fece84d8336 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();