Updating Polymer to derive from custom elements.

pkg/polymer/lib/src/build/polyfill_injector.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.
 
 /**
  * Final phase of the polymer transformation: includes any additional polyfills
  * that may needed by the deployed app.
  */
 library polymer.src.build.polyfill_injector;
 
@@ skipping 16 matching lines @@
   PolyfillInjector(this.options);
 
   /** Only run on entry point .html files. */
   Future<bool> isPrimary(Asset input) =>
       new Future.value(options.isHtmlEntryPoint(input.id));
 
   Future apply(Transform transform) {
     return readPrimaryAsHtml(transform).then((document) {
       bool shadowDomFound = false;
       bool jsInteropFound = false;
+      bool customElementFound = false;
       bool dartScriptTags = false;
 
       for (var tag in document.queryAll('script')) {
         var src = tag.attributes['src'];
         if (src != null) {
           var last = src.split('/').last;
           if (last == 'interop.js') {
             jsInteropFound = true;
           } else if (_shadowDomJS.hasMatch(last)) {
             shadowDomFound = true;
+          } else if (_customElementJS.hasMatch(last)) {
+            customElementFound = true;
           }
         }
 
         if (tag.attributes['type'] == 'application/dart') {
           dartScriptTags = true;
         }
       }
 
       if (!dartScriptTags) {
         // This HTML has no Dart code, there is nothing to do here.
         transform.addOutput(transform.primaryInput);
         return;
       }
 
       if (!jsInteropFound) {
         // JS interop code is required for Polymer CSS shimming.
         document.body.nodes.insert(0, parseFragment(
             '<script src="packages/browser/interop.js"></script>\n'));
       }
 
+      if (!customElementFound) {
+        document.body.nodes.insert(0, parseFragment(
+            '<script src="packages/custom_element/custom-elements.debug.js">'
+            '</script>\n'));
+      }
+
       if (!shadowDomFound) {
         // Insert at the beginning (this polyfill needs to run as early as
         // possible).
         // TODO(jmesserly): this is .debug to workaround issue 13046.
         document.body.nodes.insert(0, parseFragment(
             '<script src="packages/shadow_dom/shadow_dom.debug.js"></script>\n'));
       }
 
       transform.addOutput(
           new Asset.fromString(transform.primaryInput.id, document.outerHtml));
     });
   }
 }
 
 final _shadowDomJS = new RegExp(r'shadow_dom\..*\.js', caseSensitive: false);
+final _customElementJS = new RegExp(r'custom-elements\..*\.js',
+    caseSensitive: false);