Delete drawerController and make drawer handle back behavior natively

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';
 import 'package:sky/widgets/widget.dart';
 import 'package:sky/widgets/task_description.dart';
 
 import 'stock_data.dart';
 import 'stock_home.dart';
 import 'stock_settings.dart';
 import 'stock_types.dart';
 
 class StocksApp extends App {
 
   NavigationState _navigationState;
-  StocksApp();
 
   void initState() {
     _navigationState = new NavigationState([
       new Route(
         name: '/',
         builder: (navigator, route) => new StockHome(navigator, _stocks, optimismSetting, modeUpdater)
       ),
       new Route(
         name: '/settings',
         builder: (navigator, route) => new StockSettings(navigator, optimismSetting, backupSetting, settingsUpdater)
@@ skipping 62 matching lines @@
             child: new Navigator(_navigationState)
           )
         )
      );
    }
 }
 
 void main() {
   runApp(new StocksApp());
 }