Refactor stateful parts of Component into StatefulComponent

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/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';
@@ skipping 11 matching lines @@
 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);
 
-class StockHome extends Component {
+class StockHome extends StatefulComponent {
 
-  StockHome(this.navigator, this.stocks, this.stockMode, this.modeUpdater) : super(stateful: true) {
+  StockHome(this.navigator, this.stocks, this.stockMode, this.modeUpdater) {
     // if (debug)
     //   new Timer(new Duration(seconds: 1), dumpState);
     _drawerController = new DrawerController(_handleDrawerStatusChanged);
   }
 
   Navigator navigator;
   List<Stock> stocks;
   StockMode stockMode;
   ModeUpdater modeUpdater;
 
@@ skipping 228 matching lines @@
         body: buildTabNavigator(),
         snackBar: buildSnackBar(),
         floatingActionButton: buildFloatingActionButton(),
         drawer: _drawerShowing ? buildDrawer() : null
       ),
     ];
     addMenuToOverlays(overlays);
     return new Stack(overlays);
   }
 }