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

samples/polymer_intl/web/localized.html

 <!--
 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.
 -->
 <polymer-element name="localized-example">
   <template>
     <h1>Polymer Internationalized Messages Example</h1>
     
     <p>{{helloWorld}}</p>
     
     <select value="{{selectedLocale}}">
       <option value="en_US">English</option>
       <option value="fr">French</option>
       <option value="pt">Portguese</option>
     </select>
   </template>
-  <script type="application/dart;component=1" src="localized.dart"></script>
+  <script type="application/dart" src="localized.dart"></script>
 </polymer-element>