Fix spinning_mixed.dart, and resulting yak shave.

sky/sdk/example/widgets/spinning_mixed.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';
+import 'package:sky/base/scheduler.dart' as scheduler;
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/raised_button.dart';
 import 'package:sky/widgets/widget.dart';
 import 'package:vector_math/vector_math.dart';
 
 import '../rendering/solid_color_box.dart';
 
@@ skipping 19 matching lines @@
 
 Widget builder() {
   return new Flex([
       new Rectangle(const Color(0xFF00FFFF)),
       new Container(
         padding: new EdgeDims.all(10.0),
         margin: new EdgeDims.all(10.0),
         decoration: new BoxDecoration(backgroundColor: const Color(0xFFCCCCCC)),
         child: new RaisedButton(
           child: new Flex([
-            new Image(src: "https://www.dartlang.org/logos/dart-logo.png"),
+            new NetworkImage(src: "https://www.dartlang.org/logos/dart-logo.png"),
             new Text('PRESS ME'),
           ]),
           onPressed: () => print("Hello World")
         )
       ),
       new Rectangle(const Color(0xFFFFFF00)),
     ],
     direction: FlexDirection.vertical,
     justifyContent: FlexJustifyContent.spaceBetween
   );
@@ skipping 28 matching lines @@
   new RenderBoxToWidgetAdapter(proxy, builder); // adds itself to proxy
 
   addFlexChildSolidColor(flexRoot, const sky.Color(0xFFFF00FF), flex: 1);
   flexRoot.add(proxy);
   addFlexChildSolidColor(flexRoot, const sky.Color(0xFF0000FF), flex: 1);
 
   transformBox = new RenderTransform(child: flexRoot, transform: new Matrix4.identity());
   RenderPadding root = new RenderPadding(padding: new EdgeDims.all(80.0), child: transformBox);
 
   SkyBinding.instance.root = root;
-  addPersistentFrameCallback(rotate);
+  scheduler.addPersistentFrameCallback(rotate);
 }