Making Element abstract.

sdk/lib/html/dart2js/html_dart2js.dart

 library html;
 
 import 'dart:isolate';
 import 'dart:json';
 import 'dart:svg' as svg;
 // 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.
 
 // DO NOT EDIT
@@ skipping 7200 matching lines @@
   const _SimpleClientRect(this.left, this.top, this.width, this.height);
 
   bool operator ==(ClientRect other) {
     return other != null && left == other.left && top == other.top
         && width == other.width && height == other.height;
   }
 
   String toString() => "($left, $top, $width, $height)";
 }
 
-class Element extends Node implements ElementTraversal native "*Element" {
+abstract class Element extends Node implements ElementTraversal native "*Element" {
 
   factory Element.html(String html) =>
       _ElementFactoryProvider.createElement_html(html);
   factory Element.tag(String tag) =>
       _ElementFactoryProvider.createElement_tag(tag);
 
   /**
    * @domName Element.hasAttribute, Element.getAttribute, Element.setAttribute,
    *   Element.removeAttribute
    */
@@ skipping 17622 matching lines @@
     if (length < 0) throw new ArgumentError('length');
     if (start < 0) throw new RangeError.value(start);
     int end = start + length;
     if (end > a.length) throw new RangeError.value(end);
     for (int i = start; i < end; i++) {
       accumulator.add(a[i]);
     }
     return accumulator;
   }
 }