Let Dart code running in Sky add events to the trace timeline

sky/examples/stocks-fn/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/input.dart';
 import 'package:sky/framework/components/menu_divider.dart';
 import 'package:sky/framework/components/menu_item.dart';
 import 'package:sky/framework/components/popup_menu.dart';
 import 'package:sky/framework/components/scaffold.dart';
 import 'package:sky/framework/fn.dart';
 import 'package:sky/framework/theme/typography.dart' as typography;
+import 'package:sky/framework/tracing.dart';
 import 'stock_data.dart';
 import 'stock_list.dart';
 import 'stock_menu.dart';
 
 class StocksApp extends App {
 
   DrawerController _drawerController = new DrawerController();
   PopupMenuController _menuController;
 
   static Style _iconStyle = new Style('''
     padding: 8px;'''
   );
 
   static Style _titleStyle = new Style('''
     padding-left: 24px;
     flex: 1;
     ${typography.white.title};'''
   );
 
   List<Stock> _sortedStocks = [];
   bool _isSearching = false;
   bool _isShowingMenu = false;
   String _searchQuery;
 
   StocksApp() : super() {
     fetchStockOracle().then((oracle) {
       setState(() {
         _sortedStocks = oracle.stocks;
-        _sortedStocks.sort((a, b) => a.symbol.compareTo(b.symbol));
+        trace('StocksApp::sortStocks', () {
+          _sortedStocks.sort((a, b) => a.symbol.compareTo(b.symbol));
+        });
       });
     });
   }
 
   void _handleSearchClick(_) {
     setState(() {
       _isSearching = !_isSearching;
     });
   }
 
@@ skipping 97 matching lines @@
     return new Scaffold(
       actionBar: actionBar,
       content: new Stocklist(stocks: _sortedStocks, query: _searchQuery),
       fab: new FloatingActionButton(
         content: new Icon(type: 'content/add_white', size: 24), level: 3),
       drawer: drawer,
       overlays: overlays
     );
   }
 }