Refactoring to support dark theme better

sky/sdk/example/widgets/tabs.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/painting/text_style.dart';
 import 'package:sky/theme/typography.dart' as typography;
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/card.dart';
 import 'package:sky/widgets/scaffold.dart';
 import 'package:sky/widgets/tabs.dart';
@@ skipping 58 matching lines @@
         builder: () => _buildContent("Summary")
       )
     ];
     return _buildTabNavigator(n, views);
   }
 
   Container _buildCard(TabNavigator tabNavigator) {
     return new Container(
      child: new Card(child: tabNavigator),
      padding: const EdgeDims.all(12.0),
-     decoration: new BoxDecoration(backgroundColor: Theme.of(this).primary[50])
+     decoration: new BoxDecoration(backgroundColor: Theme.of(this).primarySwatch[50])
     );
   }
 
   Widget build() {
     List<TabNavigatorView> views = <TabNavigatorView>[
       new TabNavigatorView(
         label: const TabLabel(text: 'TEXT'),
         builder: () => _buildCard(_buildTextLabelsTabNavigator(0))
       ),
       new TabNavigatorView(
@@ skipping 15 matching lines @@
     return new Scaffold(
       toolbar: toolbar,
       body: tabNavigator
     );
   }
 }
 
 void main() {
   runApp(new TabbedNavigatorApp());
 }