Make _FrozenElementList generic. It's needed for some type checks.

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;
 
 // TODO(jacobr): use _Lists.dart to remove some of the duplicated
 // functionality.
 class _ChildrenElementList extends ListBase<Element> {
   // Raw Element.
@@ skipping 278 matching lines @@
     buffer.writeAll(this, ', ');
     buffer.write(']');
     return buffer.toString();
   }
 }
 
 // TODO(jacobr): this is an inefficient implementation but it is hard to see
 // a better option given that we cannot quite force NodeList to be an
 // ElementList as there are valid cases where a NodeList JavaScript object
 // contains Node objects that are not Elements.
-class _FrozenElementList extends ListBase<Element> {
+class _FrozenElementList extends ListBase {
   final List<Node> _nodeList;
 
   _FrozenElementList._wrap(this._nodeList);
 
   int get length => _nodeList.length;
 
   Element operator [](int index) => _nodeList[index];
 
   void operator []=(int index, Element value) {
     throw new UnsupportedError('');
@@ skipping 683 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');
 }