Remove keys from the examples.

sky/examples/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/app/scheduler.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/widgets/basic.dart';
@@ skipping 19 matching lines @@
     return new Flexible(
       child: new Container(
         decoration: new BoxDecoration(backgroundColor: color)
       )
     );
   }
 }
 
 Widget builder() {
   return new Flex([
-      new Rectangle(const Color(0xFF00FFFF), key: 'a'),
+      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 Text('PRESS ME'),
           ]),
           onPressed: () => print("Hello World")
         )
       ),
-      new Rectangle(const Color(0xFFFFFF00), key: 'b'),
+      new Rectangle(const Color(0xFFFFFF00)),
     ],
     direction: FlexDirection.vertical,
     justifyContent: FlexJustifyContent.spaceBetween
   );
 }
 
 double timeBase;
 RenderTransform transformBox;
 
 final TestRenderView tester = new TestRenderView();
@@ skipping 26 matching lines @@
   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(20.0), child: transformBox);
 
   WidgetAppView.appView.root = root;
   addPersistentFrameCallback(rotate);
 }