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

cc/trees/proxy_impl.h

Index: cc/trees/proxy_impl.h
diff --git a/cc/trees/proxy_impl.h b/cc/trees/proxy_impl.h
index 47c0341d7b518721f20af1f2678e6862f1b15326..9bafd11999daa9b1307a956252f4b6e60106237a 100644
--- a/cc/trees/proxy_impl.h
+++ b/cc/trees/proxy_impl.h
@@ -41,7 +41,12 @@ class CC_EXPORT ProxyImpl {
   virtual void MainFrameWillHappenOnImplForTesting(
       CompletionEvent* completion,
       bool* main_frame_will_happen) = 0;
-  virtual void StartCommitOnImpl(CompletionEvent* completion) = 0;
+  virtual void StartCommitOnImpl(CompletionEvent* completion,
+                                 LayerTreeHost* layer_tree_host,
+                                 bool hold_commit_for_activation) = 0;
+  virtual void InitializeImplOnImpl(CompletionEvent* completion,
+                                    LayerTreeHost* layer_tree_host) = 0;
+  virtual void LayerTreeHostClosedOnImpl(CompletionEvent* completion) = 0;
 
   // TODO(khushalsagar): Rename as GetWeakPtr() once ThreadProxy is split.
   virtual base::WeakPtr<ProxyImpl> GetImplWeakPtr() = 0;