Fixing custom element type extensions in Dartium to have correct native type ID

tools/dom/src/native_DOMImplementation.dart

 // Copyright (c) 2012, 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.
 
 part of html;
 
 class _ConsoleVariables {
   Map<String, Object> _data = new Map<String, Object>();
 
   /**
@@ skipping 86 matching lines @@
     if (type == other) {
       return true;
     }
     var superclass = reflectClass(type).superclass;
     if (superclass != null) {
       return isTypeSubclassOf(superclass.reflectedType, other);
     }
     return false;
   }
 
-  static bool isTypeSubclassOfTag(Type type, String tagName) {
+  static Element getAndValidateNativeType(Type type, String tagName) {
     var element = new Element.tag(tagName);
-    return isTypeSubclassOf(type, element.runtimeType);
+    if (!isTypeSubclassOf(type, element.runtimeType)) {
+      return null;
+    }
+    return element;
   }
 
   static window() native "Utils_window";
   static forwardingPrint(String message) native "Utils_forwardingPrint";
   static int _getNewIsolateId() native "Utils_getNewIsolateId";
 
   // The following methods were added for debugger integration to make working
   // with the Dart C mirrors API simpler.
   // TODO(jacobr): consider moving them to a separate library.
   // If Dart supported dynamic code injection, we would only inject this code
@@ skipping 451 matching lines @@
   _scheduleImmediateHelper._schedule(callback);
 };
 
 get _pureIsolateScheduleImmediateClosure => ((void callback()) =>
   throw new UnimplementedError("scheduleMicrotask in background isolates "
                                "are not supported in the browser"));
 
 void _initializeCustomElement(Element e) {
   _Utils.initializeCustomElement(e);
 }