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

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 e41bebace0b3e4e0dc5bf747f2edde579b54b1db..9c6689c1c4f4c6f9e993494fa725472e06df1046 100644
--- a/cc/trees/channel_main.h
+++ b/cc/trees/channel_main.h
@@ -44,7 +44,12 @@ class CC_EXPORT ChannelMain {
   virtual void SetNeedsRedrawOnImpl(const gfx::Rect& damage_rect) = 0;
   virtual void SetNeedsCommitOnImpl() = 0;
   virtual void BeginMainFrameAbortedOnImpl(CommitEarlyOutReason reason) = 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;
 
   virtual ~ChannelMain() {}
 };