Fixes needed for the deploy step.

pkg/custom_element/lib/polyfill.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.
 
 /** Dart APIs for interacting with the JavaScript Custom Elements polyfill. */
 library custom_element.polyfill;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
 
 /**
  * A future that completes once all custom elements in the initial HTML page
  * have been upgraded.
  *
  * This is needed because the native implementation can update the elements
  * while parsing the HTML document, but the custom element polyfill cannot,
  * so it completes this future once all elements are upgraded.
  */
 Future customElementsReady = () {
   if (_isReady) return new Future.value();
 
   // Not upgraded. Wait for the polyfill to fire the WebComponentsReady event.
-  return document.body.on['WebComponentsReady'].first;
+  // Note: we listen on document (not on document.body) to allow this polyfill
+  // to be loaded in the HEAD element.
+  return document.on['WebComponentsReady'].first;
 }();
 
 // Return true if we are using the polyfill and upgrade is complete, or if we
 // have native document.register and therefore the browser took care of it.
 // Otherwise return false, including the case where we can't find the polyfill.
 bool get _isReady {
   // If we don't have dart:js, assume things are ready
   if (js.context == null) return true;
 
   var customElements = js.context['CustomElements'];
   if (customElements == null) {
     // Return true if native document.register, otherwise false.
     // (Maybe the polyfill isn't loaded yet. Wait for it.)
     return document.supportsRegister;
   }
 
   return customElements['ready'] == true;
 }