Hide the accessors for bad custom element upgrade

tools/dom/templates/html/impl/impl_HTMLDocument.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.
 
 // WARNING: Do not edit - generated code.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 $!MEMBERS
@@ skipping 384 matching lines @@
       // TODO(jacobr): warning: 
       elemProto['createdCallback'] = js.JsNative.withThis(($this) {
         if (_getJSClassName(reflectClass(customElementClass).superclass) != null && creating < 2) {
           creating++;
 
           var dartClass;
           try {
             dartClass = _blink.Blink_Utils.constructElement(customElementClass, $this);
           } catch (e) {
             dartClass = HtmlElement.internalCreateHtmlElement();
-            dartClass.badUpgrade();
+            dartClass._badUpgrade();
             throw e;
           } finally {
             // Need to remember the Dart class that was created for this custom so
             // return it and setup the blink_jsObject to the $this that we'll be working
             // with as we talk to blink. 
             js.setDartHtmlWrapperFor($this, dartClass);
 
             creating--;
           }
         }
@@ skipping 71 matching lines @@
   /// parameter must be provided.
   @Experimental()
   ElementUpgrader createElementUpgrader(Type type, {String extendsTag}) {
 $if DART2JS
     return new _JSElementUpgrader(this, type, extendsTag);
 $else
     return new _VMElementUpgrader(this, type, extendsTag);
 $endif
   }
 }