Remove keys from the examples.

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/theme2/colors.dart';
 import 'package:sky/theme2/edges.dart';
@@ skipping 66 matching lines @@
       toolbar: new ToolBar(
           center: new Text('Sector Layout in a Widget Tree', style: white.title),
           backgroundColor: Blue[500]),
       body: new Material(
         edge: MaterialEdge.canvas,
         child: new Flex([
             new Container(
               padding: new EdgeDims.symmetric(horizontal: 8.0, vertical: 25.0),
               child: new Flex([
                   new RaisedButton(
-                    key: 'add-button',
                     enabled: enabledAdd,
                     child: new ShrinkWrapWidth(
                       child: new Flex([
                         new Container(
                           padding: new EdgeDims.all(4.0),
                           margin: new EdgeDims.only(right: 10.0),
                           child: new WidgetToRenderBoxAdapter(sectorAddIcon)
                         ),
                         new Text('ADD SECTOR'),
                       ])
                     ),
                     onPressed: addSector
                   ),
                   new RaisedButton(
-                    key: 'remove-button',
                     enabled: enabledRemove,
                     child: new ShrinkWrapWidth(
                       child: new Flex([
                         new Container(
                           padding: new EdgeDims.all(4.0),
                           margin: new EdgeDims.only(right: 10.0),
                           child: new WidgetToRenderBoxAdapter(sectorRemoveIcon)
                         ),
                         new Text('REMOVE SECTOR'),
                       ])
@@ skipping 23 matching lines @@
   }
 }
 
 void main() {
   runApp(new SectorApp());
   WidgetAppView.appView.onFrame = () {
     // uncomment this for debugging:
     // WidgetAppView.appView.debugDumpRenderTree();
   };
 }