Added TodoMVC startup benchmarks.

samples/third_party/todomvc_performance/web/lib-elements/polymer_localstorage.dart

 // Copyright 2013 The Polymer Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 library todomvc.web.lib_elements.polymer_localstorage;
 
 import 'dart:convert' show JSON;
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 
 // TODO(jmesserly): replace with interop to <polymer-localstorage>.
@@ skipping 20 matching lines @@
       value = JSON.decode(s);
     } else {
       value = s;
     }
   }
 
   void save() {
     window.localStorage[name] = useRaw ? value : JSON.encode(value);
   }
 }