update custom elements and shadow dom

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()
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME extends Node $NATIVESPEC
 {
 
@@ skipping 33 matching lines @@
    */
   @deprecated
   @Experimental()
   @DomName('Document.querySelectorAll')
   ElementList queryAll(String relativeSelectors) =>
       querySelectorAll(relativeSelectors);
 
   /// Checks if [register] is supported on the current platform.
   bool get supportsRegister {
 $if DART2JS
-    return JS('bool', '("register" in #)', this);
+    return JS('bool', '("registerElement" in #)', this);
 $else
     return true;
 $endif
   }
 
   @DomName('Document.createElement')
   Element createElement(String tagName, [String typeExtension]) {
 $if DART2JS
     return _createElement(tagName, typeExtension);
 $else
     if (typeExtension != null) {
       return _createElement(tagName, typeExtension);
     } else {
       // Fast-path for Dartium when typeExtension is not needed.
       return _Utils.createElement(this, tagName);
     }
 $endif
   }
 }