Cleanup of SkyBinding, and resultant yak shaving.

sky/examples/stocks2/lib/stock_app.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 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/navigator.dart';
 import 'package:sky/widgets/widget.dart';
 
 import 'stock_home.dart';
 import 'stock_settings.dart';
 
 class StocksApp extends App {
 
   NavigationState _navState = new NavigationState([
@@ skipping 13 matching lines @@
   }
 
   Widget build() {
     return new Navigator(_navState);
   }
 }
 
 void main() {
   print("starting stocks app!");
   runApp(new StocksApp());
-  WidgetSkyBinding.skyBinding.onFrame = () {
+  SkyBinding.instance.onFrame = () {
     // uncomment this for debugging:
-    // WidgetSkyBinding.skyBinding.debugDumpRenderTree();
+    // SkyBinding.instance.debugDumpRenderTree();
   };
 }