Add List.asMap().

tools/dom/src/WrappedList.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.
 
 part of dart.dom.html;
 
 /**
  * A list which just wraps another list, for either intercepting list calls or
  * retyping the list (for example, from List<A> to List<B> where B extends A).
  */
@@ skipping 106 matching lines @@
 
   void setRange(int start, int length, List<E> from, [int startFrom]) {
     _list.setRange(start, length, from, startFrom);
   }
 
   void removeRange(int start, int length) { _list.removeRange(start, length); }
 
   void insertRange(int start, int length, [E fill]) {
     _list.insertRange(start, length, fill);
   }
+
+  Map<int, E> asMap() => IterableMixinWorkaround.asMapList(_list);
 }
 
 /**
  * Iterator wrapper for _WrappedList.
  */
 class _WrappedIterator<E> implements Iterator<E> {
   Iterator _iterator;
 
   _WrappedIterator(this._iterator);
 
   bool moveNext() {
     return _iterator.moveNext();
   }
 
   E get current => _iterator.current;
 }