[Effen] fix warnings

remove members that are never read
remove imports that are never used

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1099203002

examples/stocks/lib/stock_app.dart

@@ -14,7 +14,6 @@ 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';
@@ -35,14 +34,12 @@ class StocksApp extends App {
   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);
       });

examples/stocks/lib/stock_data.dart

@@ -4,7 +4,6 @@
 
 import 'dart:convert';
 import 'dart:math';
-import 'package:sky/framework/debug/tracing.dart';
 import 'package:sky/framework/net/fetch.dart';
 
 // Snapshot from http://www.nasdaq.com/screening/company-list.aspx

examples/stocks/lib/stock_list.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:sky/framework/animation/scroll_behavior.dart';
 import 'package:sky/framework/components/fixed_height_scrollable.dart';
 import 'package:sky/framework/fn.dart';
 import 'stock_data.dart';