Remove onFrame callback

sky/sdk/lib/rendering/sky_binding.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:sky' as sky;
 
 import 'package:sky/base/scheduler.dart' as scheduler;
 import 'package:sky/base/hit_test.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
@@ skipping 47 matching lines @@
   RenderView _renderView;
   RenderView get renderView => _renderView;
 
   ViewConstraints _createConstraints() {
     return new ViewConstraints(size: new Size(sky.view.width, sky.view.height));
   }
   void _handleMetricsChanged() {
     _renderView.rootConstraints = _createConstraints();
   }
 
-  Function onFrame;
   RenderBox get root => _renderView.child;
   void set root(RenderBox value) {
     _renderView.child = value;
   }
   void _beginFrame(double timeStamp) {
-    if (onFrame != null)
-      onFrame();
     RenderObject.flushLayout();
     RenderObject.flushPaint();
     _renderView.paintFrame();
   }
 
   final List<EventListener> _eventListeners = new List<EventListener>();
   void addEventListener(EventListener e) => _eventListeners.add(e);
   bool removeEventListener(EventListener e) => _eventListeners.remove(e);
 
   void _handleEvent(sky.Event event) {
@@ skipping 53 matching lines @@
       entry.target.handleEvent(event, entry);
   }
 
   String toString() => 'Render Tree:\n${_renderView}';
 
   void debugDumpRenderTree() {
     toString().split('\n').forEach(print);
   }
 
 }