cc: Send shared variables between main and impl side using the channel

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 76c7516168e5c1cfbfb000b42f8176e4159c30be..1a4b8b7027ad2acf883fc730def38235f6701a94 100644
--- a/cc/trees/threaded_channel.h
+++ b/cc/trees/threaded_channel.h
@@ -96,7 +96,12 @@ class CC_EXPORT ThreadedChannel : public ChannelMain, public ChannelImpl {
   void MainFrameWillHappenOnImplForTesting(
       CompletionEvent* completion,
       bool* main_frame_will_happen) override;
-  void StartCommitOnImpl(CompletionEvent* completion) override;
+  void StartCommitOnImpl(CompletionEvent* completion,
+                         LayerTreeHost* layer_tree_host,
+                         bool hold_commit_for_activation) override;
+  void InitializeImplOnImpl(CompletionEvent* completion,
+                            LayerTreeHost* layer_tree_host) override;
+  void LayerTreeHostClosedOnImpl(CompletionEvent* completion) override;
 
   // ChannelImpl Implementation
   void DidCompleteSwapBuffers() override;