Make rendering use PaintingNodes for increased efficiency.

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 '../base/scheduler.dart' as scheduler;
 import '../base/hit_test.dart';
 import 'box.dart';
 import 'object.dart';
@@ skipping 45 matching lines @@
 
   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) {
     if (event is sky.PointerEvent) {
       _handlePointerEvent(event);
@@ skipping 50 matching lines @@
       entry.target.handleEvent(event, entry);
   }
 
   String toString() => 'Render Tree:\n${_renderView}';
 
   void debugDumpRenderTree() {
     toString().split('\n').forEach(print);
   }
   
 }