Material light and dark themes for Sky widgets

sky/sdk/lib/widgets/theme.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/theme_data.dart';
 import 'basic.dart';
 import 'widget.dart';
 
 class Theme extends Inherited {
 
   Theme({
     String key,
     this.data,
     Widget child
   }) : super(key: key, child: child) {
     assert(child != null);
     assert(data != null);
   }
 
   final ThemeData data;
 
+  static ThemeData _kFallbackTheme = new ThemeData.fallback();

[abarth-chromium, 2015/06/23 02:11:36]

final

[jackson, 2015/06/23 17:14:09]

Fixed in https://codereview.chromium.org/1192773004

+
   static ThemeData of(Component component) {
     Theme theme = component.inheritedOfType(Theme);
-    // If you hit this assert, you need to wrap your Component in a Theme
-    assert(theme != null);
-    return theme.data;
+    return theme == null ? _kFallbackTheme : theme.data;
   }
 }