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 8acbb97377e108ce58d5849b55c47ca131d35709..c1598cc595cdfa09c66dd91464b072a5e78085f1 100644
--- a/cc/trees/proxy_impl.h
+++ b/cc/trees/proxy_impl.h
@@ -43,7 +43,12 @@ 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;