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

cc/trees/remote_channel_main.h

Index: cc/trees/remote_channel_main.h
diff --git a/cc/trees/remote_channel_main.h b/cc/trees/remote_channel_main.h
index 1848f5c589cbffa05772be0bd85b8b90b24db685..6b9041b36bf26a9e237db1942fc234b01cfdd6de 100644
--- a/cc/trees/remote_channel_main.h
+++ b/cc/trees/remote_channel_main.h
@@ -34,6 +34,7 @@ class CC_EXPORT RemoteChannelMain : public ChannelMain,
                                     TopControlsState current,
                                     bool animate) override;
   void InitializeOutputSurfaceOnImpl(OutputSurface* output_surface) override;
+  void InitializeMutatorOnImpl(LayerTreeMutator* mutator) override;
   void MainThreadHasStoppedFlingingOnImpl() override;
   void SetInputThrottledUntilCommitOnImpl(bool is_throttled) override;
   void SetDeferCommitsOnImpl(bool defer_commits) override;