Remove keys from the examples.

sky/examples/widgets/navigation.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/widgets/basic.dart';
 import 'package:sky/widgets/navigator.dart';
 import 'package:sky/widgets/transition.dart';
 import 'package:sky/widgets/raised_button.dart';
 
 List<Route> routes = [
   new Route(
     name: 'home',
     builder: (navigator) => new Container(
       padding: const EdgeDims.all(20.0),
       decoration: new BoxDecoration(backgroundColor: const Color(0xFFCCCCCC)),
       child: new Block([
         new Text("You are at home"),
         new RaisedButton(
-          key: 'b',
           child: new Text('GO SHOPPING'),
           onPressed: () => navigator.pushNamed('shopping')
         ),
         new RaisedButton(
-          key: 'a',
           child: new Text('START ADVENTURE'),
           onPressed: () => navigator.pushNamed('adventure')
         )
       ])
     )
   ),
   new Route(
     name: 'shopping',
     builder: (navigator) => new Container(
       padding: const EdgeDims.all(20.0),
       decoration: new BoxDecoration(backgroundColor: const Color(0xFFBF5FFF)),
       child: new Block([
         new Text("Village Shop"),
         new RaisedButton(
-          key: 'a',
           child: new Text('RETURN HOME'),
           onPressed: () => navigator.back()
         ),
         new RaisedButton(
-          key: 'b',
           child: new Text('GO TO DUNGEON'),
           onPressed: () => navigator.push(routes[2])
         )
       ])
     )
   ),
   new Route(
     name: 'adventure',
     builder: (navigator) => new Container(
       padding: const EdgeDims.all(20.0),
@@ skipping 13 matching lines @@
   NavigationState _navState = new NavigationState(routes);
 
   Widget build() {
     return new Flex([new Navigator(_navState)]);
   }
 }
 
 void main() {
   runApp(new NavigationExampleApp());
 }