[Effen] fix warnings

sky/examples/stocks/lib/stock_app.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/framework/components/action_bar.dart';
 import 'package:sky/framework/components/drawer.dart';
 import 'package:sky/framework/components/drawer_header.dart';
 import 'package:sky/framework/components/floating_action_button.dart';
 import 'package:sky/framework/components/icon.dart';
 import 'package:sky/framework/components/icon_button.dart';
 import 'package:sky/framework/components/input.dart';
 import 'package:sky/framework/components/menu_divider.dart';
 import 'package:sky/framework/components/menu_item.dart';
 import 'package:sky/framework/components/modal_overlay.dart';
 import 'package:sky/framework/components/popup_menu.dart';
 import 'package:sky/framework/components/scaffold.dart';
-import 'package:sky/framework/debug/tracing.dart';
 import 'package:sky/framework/fn.dart';
 import 'package:sky/framework/theme/typography.dart' as typography;
 import 'package:sky/framework/theme/colors.dart';
 import 'stock_data.dart';
 import 'stock_list.dart';
 import 'stock_menu.dart';
 
 class StocksApp extends App {
   DrawerController _drawerController = new DrawerController();
   PopupMenuController _menuController;
 
   static final Style _actionBarStyle = new Style('''
     background-color: ${Purple[500]};''');
 
   static final Style _searchBarStyle = new Style('''
     background-color: ${Grey[50]};''');
 
   static final Style _titleStyle = new Style('''
     ${typography.white.title};''');
 
-  StockDataFetcher _stockDataFetcher;
   List<Stock> _stocks = [];
   bool _isSearching = false;
-  bool _isShowingMenu = false;
   String _searchQuery;
 
   StocksApp() : super() {
-    _stockDataFetcher = new StockDataFetcher((StockData data) {
+    new StockDataFetcher((StockData data) {
       setState(() {
         data.appendTo(_stocks);
       });
     });
   }
 
   void _handleSearchBegin(_) {
     setState(() {
       _isSearching = true;
     });
@@ skipping 105 matching lines @@
     return new Scaffold(
       header: _isSearching ? buildSearchBar() : buildActionBar(),
       content: new Stocklist(stocks: _stocks, query: _searchQuery),
       fab: new FloatingActionButton(
         content: new Icon(type: 'content/add_white', size: 24), level: 3),
       drawer: buildDrawer(),
       overlays: overlays
     );
   }
 }