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

pkg/polymer/test/events_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 polymer.test.web.events_test;
 
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 import 'package:unittest/html_config.dart';
 import 'package:unittest/unittest.dart';
@@ skipping 26 matching lines @@
   void clickHandler(e) {
     clicks.add('local click under $localName (id $id) on ${e.target.id}');
   }
 }
 
 @CustomTag("test-c")
 class TestC extends TestBase {
   TestC.created() : super.created();
 }
 
-@initMethod
-main() {
+main() => initPolymer().run(() {
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('host event', () {
     // Note: this test is currently the only event in
     // polymer/test/js/events.js at commit #7936ff8
     var testA = querySelector('#a');
     expect(testA.clicks, isEmpty);
     testA.click();
@@ skipping 18 matching lines @@
     expect(testC.clicks, isEmpty);
     testC.click();
     expect(testC.clicks, []);
     var c1 = testC.shadowRoot.querySelector('#c-1');
     c1.click();
     expect(testC.clicks, []);
     var c2 = testC.shadowRoot.querySelector('#c-2');
     c2.click();
     expect(testC.clicks, ['local click under test-c (id c) on c-2']);
   });
-}
+});