Update TodoMVC based on https://github.com/polymer/todomvc

samples/third_party/todomvc/web/app.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-// for details. 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.app;
-
-import 'dart:html';
-import 'package:polymer/polymer.dart';
-import 'model.dart';
-
-@CustomTag('todo-app')
-class TodoApp extends PolymerElement {
-  @observable AppModel app;
-  bool get applyAuthorStyles => true;
-
-  factory TodoApp() => new Element.tag('TodoApp');
-
-  TodoApp.created() : super.created() {
-    app = appModel;
-  }
-
-  void addTodo(Event e) {
-    e.preventDefault(); // don't submit the form
-    InputElement input = getShadowRoot('todo-app').query('#new-todo');
-    if (input.value == '') return;
-    app.todos.add(new Todo(input.value));
-    input.value = '';
-  }
-
-  void clear() => app.clearDone();
-}