Bring back initPolymer, allow boot.js only if using "polymer_experimental.html".

samples/third_party/todomvc/test/mainpage_test.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.test.mainpage_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
 import 'package:polymer/polymer.dart';
 import 'package:unittest/html_config.dart';
 import 'package:unittest/unittest.dart';
 import '../web/elements/td_model.dart';
 import '../web/elements/td_todos.dart';
 import 'utils.dart';
 
 /**
  * This test runs the TodoMVC app and checks the state of the initial page.
  */
-@initMethod
 main() {
+  initPolymer();
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('initial state', () {
     final model = querySelector('td-model');
     expect(model is TodoModel, true, reason: 'TodoModel should be created');
 
     final app = querySelector('td-todos');
     expect(app is TodoList, true, reason: 'TodoList should be created');
@@ skipping 17 matching lines @@
     // Validate a style got applied
     var color = root.querySelector('#footer').getComputedStyle().color;
     expect(color, 'rgb(119, 119, 119)');
 
     return onPropertyInit(model, 'items').then((_) {
       expect(model.items, [], reason: 'no items yet');
       expect(app.model, model, reason: 'model should be data-bound');
     });
   });
 }