Allow Object when doing lookups.

tools/dom/templates/html/impl/impl_Element.darttemplate

 // 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 $LIBRARYNAME;
 
 class _ChildrenElementList extends ListBase<Element> {
   // Raw Element.
   final Element _element;
   final HtmlCollection _childElements;
 
   _ChildrenElementList._wrap(Element element)
     : _childElements = element.$dom_children,
       _element = element;
 
-  bool contains(Element element) => _childElements.contains(element);
+  bool contains(Object element) => _childElements.contains(element);
 
 
   bool get isEmpty {
     return _element.$dom_firstElementChild == null;
   }
 
   int get length {
     return _childElements.length;
   }
 
@@ skipping 1036 matching lines @@
   const ScrollAlignment._internal(this._value);
   toString() => 'ScrollAlignment.$_value';
 
   /// Attempt to align the element to the top of the scrollable area.
   static const TOP = const ScrollAlignment._internal('TOP');
   /// Attempt to center the element in the scrollable area.
   static const CENTER = const ScrollAlignment._internal('CENTER');
   /// Attempt to align the element to the bottom of the scrollable area.
   static const BOTTOM = const ScrollAlignment._internal('BOTTOM');
 }