cc: Get BeginFrameArgs for STP::BeginMainFrame while inside an impl frame.

cc/trees/single_thread_proxy.h

Index: cc/trees/single_thread_proxy.h
diff --git a/cc/trees/single_thread_proxy.h b/cc/trees/single_thread_proxy.h
index 99ef009e60fc9275dc9db88c3ba2c15b565154e0..cd80a1cf6dc598cf666e0443ffe1739f41da2518 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -129,7 +129,7 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
       scoped_ptr<BeginFrameSource> external_begin_frame_source);
 
  private:
-  void BeginMainFrame();
+  void BeginMainFrame(const BeginFrameArgs& begin_frame_args);
   void BeginMainFrameAbortedOnImplThread(CommitEarlyOutReason reason);
   void DoAnimate();
   void DoBeginMainFrame(const BeginFrameArgs& begin_frame_args);
@@ -160,6 +160,7 @@ class CC_EXPORT SingleThreadProxy : public Proxy,
   scoped_ptr<ResourceUpdateQueue> queue_for_commit_;
   bool next_frame_is_newly_committed_frame_;
 
+  bool inside_impl_frame_;
   bool inside_draw_;
   bool defer_commits_;
   bool animate_requested_;