Cleanup of SkyBinding, and resultant yak shaving.

sky/examples/widgets/sector.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:math' as math;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
+import 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/theme2/colors.dart';
 import 'package:sky/theme2/edges.dart';
 import 'package:sky/theme2/typography.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/material.dart';
 import 'package:sky/widgets/raised_button.dart';
 import 'package:sky/widgets/scaffold.dart';
 import 'package:sky/widgets/tool_bar.dart';
 import 'package:sky/widgets/widget.dart';
 
@@ skipping 110 matching lines @@
           direction: FlexDirection.vertical,
           justifyContent: FlexJustifyContent.spaceBetween
         )
       )
     );
   }
 }
 
 void main() {
   runApp(new SectorApp());
-  WidgetSkyBinding.skyBinding.onFrame = () {
+  SkyBinding.instance.onFrame = () {
     // uncomment this for debugging:
-    // WidgetSkyBinding.skyBinding.debugDumpRenderTree();
+    // SkyBinding.instance.debugDumpRenderTree();
   };
 }