Refactoring to support dark theme better

sky/sdk/example/stocks/lib/main.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/theme/colors.dart' as colors;
 import 'package:sky/theme/typography.dart' as typography;
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/default_text_style.dart';
 import 'package:sky/widgets/navigator.dart';
 import 'package:sky/widgets/theme.dart';
@@ skipping 50 matching lines @@
       setState(() {
         data.appendTo(_stocks);
       });
     });
   }
 
   Widget build() {
 
     ThemeData theme;
     if (optimismSetting == StockMode.optimistic) {
-      theme = new ThemeData.light(
-        primary: colors.Purple,
-        accent: colors.RedAccent,
-        darkToolbar: true
+      theme = new ThemeData(
+        brightness: ThemeBrightness.light,
+        primarySwatch: colors.Purple,
+        accentColor: colors.RedAccent[200]
       );
     } else {
-      theme = new ThemeData.dark(
-        primary: colors.Red,
-        accent: colors.PurpleAccent
+      theme = new ThemeData(
+        brightness: ThemeBrightness.dark,
+        accentColor: colors.RedAccent[200]
       );
     }
 
     return new Theme(
       data: theme,
         child: new DefaultTextStyle(
           style: typography.error, // if you see this, you've forgotten to correctly configure the text style!
           child: new Navigator(_navigationState)
         )
      );
    }
 }
 
 void main() {
   runApp(new StocksApp());
 }