Fixing element_types_test/supported_object

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 implements List {
   // Raw Element.
@@ skipping 1010 matching lines @@
     if (list.length == 1) return list[0];
     throw new ArgumentError('HTML had ${list.length} '
         'top level elements but 1 expected');
   }
 
   @DomName('Document.createElement')
 $if DART2JS
   // Optimization to improve performance until the dart2js compiler inlines this
   // method.
   static dynamic createElement_tag(String tag) =>
-      JS('Element', 'document.createElement(#)', tag);
+      JS('Element|Function', 'document.createElement(#)', tag);

[sra1, 2013/02/04 22:46:37]

I'd write

// Firefox may return a JavaScript function which is no really any Dart type.
// =Object is the closes approximation to this.
JS('Element|=Object', ...)

 $else
   static Element createElement_tag(String tag) =>
       document.$dom_createElement(tag);
 $endif
 }