WIP - compositor worker mega patch.

cc/trees/channel_main.h

Index: cc/trees/channel_main.h
diff --git a/cc/trees/channel_main.h b/cc/trees/channel_main.h
index 39861e054ef4287c313d49315cffd364c9663e7c..c27ac679f729196a1db46a12084caa112c8689f8 100644
--- a/cc/trees/channel_main.h
+++ b/cc/trees/channel_main.h
@@ -15,6 +15,8 @@
 
 namespace cc {
 
+class LayerTreeMutator;
+
 // ChannelMain and ChannelImpl provide an abstract communication layer for
 // the main and impl side of the compositor.
 //
@@ -35,6 +37,7 @@ class CC_EXPORT ChannelMain {
                                             TopControlsState current,
                                             bool animate) = 0;
   virtual void InitializeOutputSurfaceOnImpl(OutputSurface* output_surface) = 0;
+  virtual void InitializeMutatorOnImpl(LayerTreeMutator* mutator) = 0;
   virtual void MainThreadHasStoppedFlingingOnImpl() = 0;
   virtual void SetInputThrottledUntilCommitOnImpl(bool is_throttled) = 0;
   virtual void SetDeferCommitsOnImpl(bool defer_commits) = 0;