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

samples/third_party/todomvc/test/markdone_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.markdone_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 import 'package:unittest/unittest.dart';
@@ skipping 14 matching lines @@
     var r = findWithText(n, text);
     if (r != null) return r;
   }
   return null;
 }
 
 /**
  * This test runs the TodoMVC app, adds a few todos, marks some as done
  * programatically, and clicks on a checkbox to mark others via the UI.
  */
-@initMethod
 main() {
+  initPolymer();
   useHtmlConfiguration();
 
   TodoModel model;
 
   setUp(() => Polymer.onReady.then((_) {
     model = querySelector('td-model');
     return onPropertyInit(model, 'items');
   }));
 
   test('mark done', () {
@@ skipping 13 matching lines @@
       var node = host.querySelector('input');
       expect(node is InputElement, true, reason: 'node is a checkbox');
       expect(node.type, 'checkbox', reason: 'node type is checkbox');
       expect(node.checked, isFalse, reason: 'element is unchecked');
 
       node.dispatchEvent(new MouseEvent('click', detail: 1));
       expect(node.checked, true, reason: 'element is checked');
     });
   });
 }