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

pkg/polymer/test/unbind_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.unbind_test;
 
 import 'dart:async' show Future, scheduleMicrotask;
 import 'dart:html';
 
 @MirrorsUsed(targets: const [Polymer], override: 'polymer.test.unbind_test')
@@ skipping 21 matching lines @@
     fooWasChanged = true;
   }
 
   barChanged() {
     validBar = bar;
   }
 
   bool get isBarValid => validBar == bar;
 }
 
-@initMethod
-main() {
+main() => initPolymer().run(() {
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('unbind', unbindTests);
-}
+});
 
 Future testAsync(List<Function> tests, int delayMs, [List args]) {
   if (tests.length == 0) return new Future.value();
   // TODO(jmesserly): CustomElements.takeRecords();
   return new Future.delayed(new Duration(milliseconds: delayMs), () {
     if (args == null) args = [];
     var lastArgs = Function.apply(tests.removeAt(0), args);
     return testAsync(tests, delayMs, lastArgs);
   });
 }
@@ skipping 46 matching lines @@
   }).then(delay).then((node) {
     expect(_unbound(node), null, reason:
         'element is bound when manually inserted');
     node.remove();
     return node;
   }).then(delay).then((node) {
     expect(_unbound(node), true, reason:
         'element is unbound when manually removed is called');
   });
 }