Use proper type in _createElement_2

tools/dom/templates/html/impl/impl_Document.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;
 
 @DocsEditable()
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME extends Node
 {
 
@@ skipping 74 matching lines @@
     }
 
     return wrapped;
 $endif
   }
 
 $if DART2JS
   // The two-argument version of this is automatically generated, but we need to
   // omit the typeExtension if it's null on Firefox or we get an is="null" attribute.
   @DomName('Document.createElement')
-  _createElement_2(String tagName) => JS('', '#.createElement(#)', this, tagName);
+  _createElement_2(String tagName) =>
+      JS('Element', '#.createElement(#)', this, tagName);
 
   // The three-argument version of this is automatically generated, but we need to
   // omit the typeExtension if it's null on Firefox or we get an is="null" attribute.
   @DomName('Document.createElementNS')
   _createElementNS_2(String namespaceURI, String qualifiedName) =>
-      JS('', '#.createElementNS(#, #)', this, namespaceURI, qualifiedName);
+      JS('Element', '#.createElementNS(#, #)', this, namespaceURI, qualifiedName);
 
 $endif
   @DomName('Document.createElementNS')
   @DocsEditable()
   Element createElementNS(String namespaceURI, String qualifiedName, [String typeExtension]) {
 $if DART2JS
     return (typeExtension == null)
         ? _createElementNS_2(namespaceURI, qualifiedName)
         : _createElementNS(namespaceURI, qualifiedName, typeExtension);
 $else
@@ skipping 26 matching lines @@
       => JS('NodeIterator', '#.createNodeIterator(#, #, #, false)',
           this, root, whatToShow, filter);
 
   @DomName('Document.createTreeWalker')
   TreeWalker _createTreeWalker(Node root,
       [int whatToShow, NodeFilter filter])
       => JS('TreeWalker', '#.createTreeWalker(#, #, #, false)',
           this, root, whatToShow, filter);
 $endif
 }