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

pkg/polymer/test/event_path_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.event_path_test;
 
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 import 'package:unittest/html_config.dart';
 import 'package:unittest/unittest.dart';
 
 class XSelector extends PolymerElement {
   XSelector.created() : super.created();
 }
 
 class XOverlay extends PolymerElement {
   XOverlay.created() : super.created();
 }
 
 class XMenu extends PolymerElement {
   XMenu.created() : super.created();
 }
 
 class XMenuButton extends PolymerElement {
   XMenuButton.created() : super.created();
 }
 
-@initMethod
-main() {
+main() => initPolymer().run(() {
+  useHtmlConfiguration();
+
   // TODO(sigmund): use @CustomTag instead of Polymer.regsiter. A bug is making
   // this code sensitive to the order in which we register elements (e.g. if
   // x-menu is registered before x-selector). See dartbug.com/17926.
   Polymer.register('x-selector', XSelector);
   Polymer.register('x-overlay', XOverlay);
   Polymer.register('x-menu', XMenu);
   Polymer.register('x-menu-button', XMenuButton);
 
-  useHtmlConfiguration();
-
   setUp(() => Polymer.onReady);
 
   test('bubbling in the right order', () {
     var item1 = querySelector('#item1');
     var menuButton = querySelector('#menuButton');
     // Note: polymer uses automatic node finding (menuButton.$.menu)
     // also note that their node finding code also reachs into the ids
     // from the parent shadow (menu.$.selectorContent instead of
     // menu.$.menuShadow.$.selectorContent)
     var menu = menuButton.shadowRoot.querySelector('#menu');
@@ skipping 24 matching lines @@
       var node = expectedPath[i];
       expect(node, isNotNull, reason: "Should not be null at $i");
       node.on['x'].listen(expectAsync((e) {
         expect(e.currentTarget, node);
         expect(x++, i);
       }));
     }
 
     item1.dispatchEvent(new Event('x', canBubble: true));
   });
-}
+});