cc: Implement unified BeginFrame on aura

cc/trees/proxy.h

Index: cc/trees/proxy.h
diff --git a/cc/trees/proxy.h b/cc/trees/proxy.h
index 539effeda7a9588414adeea6061c67e3c79e199d..abd0f1844a6981b75861b72bc1e7fab77529679d 100644
--- a/cc/trees/proxy.h
+++ b/cc/trees/proxy.h
@@ -109,6 +109,9 @@ class CC_EXPORT Proxy {
 
   virtual void SetChildrenNeedBeginFrames(bool children_need_begin_frames) = 0;
 
+  virtual void SetAuthoritativeVSyncInterval(
+      const base::TimeDelta& interval) = 0;
+
   // Testing hooks
   virtual bool MainFrameWillHappenForTesting() = 0;