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

pkg/polymer/test/event_handlers_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.event_handlers_test;
 
 import 'dart:async';
 import 'dart:html';
 
 import 'package:polymer/polymer.dart';
@@ skipping 78 matching lines @@
   XTest _element;
   @observable final int index;
   @reflectable void itemTapAction(e, d, n) {
     _element._logEvent(e, 'mini-model callback $this');
     e.stopPropagation();
   }
   MiniModel(this._element, this.index);
   String toString() => "<mini-model $index>";
 }
 
-@initMethod main() {
+main() => initPolymer();
+
+@initMethod init() {
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
   test('events handled', () {
     XTest test = querySelector('x-test');
     expect(test._onTestDone, isNotNull, reason: 'ready was called');
     return test._onTestDone;
   });
 }