Update CustomElement as well.

pkg/custom_element/lib/custom_element.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.
 
 /**
  * Custom Elements let authors define their own elements. Authors associate code
  * with custom tag names, and then use those custom tag names as they would any
  * standard tag. See <www.polymer-project.org/platform/custom-elements.html>
  * for more information.
  */
@@ skipping 453 matching lines @@
   int get scrollLeft => host.scrollLeft;
 
   int get scrollTop => host.scrollTop;
 
   set scrollLeft(int value) { host.scrollLeft = value; }
 
   set scrollTop(int value) { host.scrollTop = value; }
 
   int get scrollWidth => host.scrollWidth;
 
-  String $dom_getAttribute(String name) =>
-      host.$dom_getAttribute(name);
-
-  String $dom_getAttributeNS(String namespaceUri, String localName) =>
-      host.$dom_getAttributeNS(namespaceUri, localName);
-
-  String $dom_setAttributeNS(
-      String namespaceUri, String localName, String value) {
-    host.$dom_setAttributeNS(namespaceUri, localName, value);
-  }
-
   Rect getBoundingClientRect() => host.getBoundingClientRect();
 
   List<Rect> getClientRects() => host.getClientRects();
 
   List<Node> getElementsByClassName(String name) =>
       host.getElementsByClassName(name);
 
-  void $dom_setAttribute(String name, String value) =>
-      host.$dom_setAttribute(name, value);
-
-  List<Node> get $dom_childNodes => host.$dom_childNodes;
-
   Node get firstChild => host.firstChild;
 
   Node get lastChild => host.lastChild;
 
   String get localName => host.localName;
 
   String get namespaceUri => host.namespaceUri;
 
   int get nodeType => host.nodeType;
 
@@ skipping 118 matching lines @@
       for (var removed in record.removedNodes) {
         if (identical(node, removed)) {
           observer.disconnect();
           element.removed();
           return;
         }
       }
     }
   }).observe(element.parentNode, childList: true);
 }