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

cc/trees/threaded_channel.h

Index: cc/trees/threaded_channel.h
diff --git a/cc/trees/threaded_channel.h b/cc/trees/threaded_channel.h
index 46b7d5f460f5147e16239129fa77c1bf2428d6f3..7ec2be1d2d6bf4cafc98b705d6191519735ed2aa 100644
--- a/cc/trees/threaded_channel.h
+++ b/cc/trees/threaded_channel.h
@@ -88,6 +88,7 @@ class CC_EXPORT ThreadedChannel : public ChannelMain, public ChannelImpl {
                                     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;