Refactoring to support dark theme better

sky/sdk/example/stocks/lib/stock_home.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/editing/input.dart';
-import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/drawer.dart';
 import 'package:sky/widgets/drawer_header.dart';
 import 'package:sky/widgets/floating_action_button.dart';
 import 'package:sky/widgets/icon.dart';
 import 'package:sky/widgets/icon_button.dart';
 import 'package:sky/widgets/menu_divider.dart';
 import 'package:sky/widgets/menu_item.dart';
 import 'package:sky/widgets/modal_overlay.dart';
 import 'package:sky/widgets/navigator.dart';
 import 'package:sky/widgets/popup_menu.dart';
 import 'package:sky/widgets/radio.dart';
 import 'package:sky/widgets/scaffold.dart';
 import 'package:sky/widgets/tabs.dart';
+import 'package:sky/widgets/theme.dart';
 import 'package:sky/widgets/tool_bar.dart';
 import 'package:sky/widgets/widget.dart';
 
 import 'stock_data.dart';
 import 'stock_list.dart';
 import 'stock_menu.dart';
 import 'stock_types.dart';
 
 typedef void ModeUpdater(StockMode mode);
 
@@ skipping 181 matching lines @@
   // TODO(abarth): Should we factor this into a SearchBar in the framework?
   Widget buildSearchBar() {
     return new ToolBar(
       left: new IconButton(
         icon: 'navigation/arrow_back_grey600',
         onPressed: _handleSearchEnd),
       center: new Input(
         focused: true,
         placeholder: 'Search stocks',
         onChanged: _handleSearchQueryChanged),
-      backgroundColor: colors.Grey[50]
+      backgroundColor: Theme.of(this).canvasColor
     );
   }
 
   void addMenuToOverlays(List<Widget> overlays) {
     if (_menuController == null)
       return;
     overlays.add(new ModalOverlay(
       children: [new StockMenu(
         controller: _menuController,
         autorefresh: _autorefresh,
@@ skipping 10 matching lines @@
         floatingActionButton: new FloatingActionButton(
           child: new Icon(type: 'content/add_white', size: 24)
         ),
         drawer: _drawerShowing ? buildDrawer() : null
       ),
     ];
     addMenuToOverlays(overlays);
     return new Stack(overlays);
   }
 }