Hide the accessors for bad custom element upgrade

tools/dom/templates/html/dartium/html_dartium.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.
 
 // DO NOT EDIT
 // Auto-generated dart:html library.
 
 /**
  * HTML elements and other resources for web-based applications that need to
  * interact with the browser and the DOM (Document Object Model).
@@ skipping 557 matching lines @@
 
     // Problem?
     return null;
   }
 }
 
 // Upgrade a Dart HtmlElement to the user's Dart custom element class.
 _upgradeHtmlElement(dartInstance) {
   // Only try upgrading HtmlElement (Dart class) if there is a failure then
   // don't try it again - one failure is enough.
-  if (dartInstance.runtimeType == HtmlElement && !dartInstance.isBadUpgrade) {
+  if (dartInstance.runtimeType == HtmlElement && !dartInstance._isBadUpgrade) {
     // Must be exactly HtmlElement not something derived from it.
     var jsObject = dartInstance.blink_jsObject;
     var localName = dartInstance.localName;
     var customElementClass = _knownCustomeElements[localName];
     // Custom Element to upgrade.
     if (customElementClass != null) {
       try {
         dartInstance = _blink.Blink_Utils.constructElement(customElementClass, jsObject);
       } catch (e) {
-        dartInstance.badUpgrade();
+        dartInstance._badUpgrade();
       } finally {
         dartInstance.blink_jsObject = jsObject;
         jsObject['dart_class'] = dartInstance;
         js.setDartHtmlWrapperFor(jsObject, dartInstance);
      }
    }
   }
 
   return dartInstance;
 }
@@ skipping 79 matching lines @@
 }
 
 /**
  * Upgrade the JS HTMLElement to the Dart class.  Used by Dart's Polymer.
  */
 createCustomUpgrader(Type customElementClass, $this) {
   var dartClass;
   try {
     dartClass = _blink.Blink_Utils.constructElement(customElementClass, $this);
   } catch (e) {
-    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);
   }
 
   return dartClass;
 }
 
 $else
 class DartHtmlDomObject extends NativeFieldWrapperClass2 {}
 
 unwrap_jso(dartClass_instance) => dartClass_instance;
 wrap_jso(jsObject) => jsObject;
 make_dart_rectangle(r) => r;
 convertDartToNative_Dictionary(Map dict) => dict;
 List convertDartToNative_StringArray(List<String> input) => input;
 convertDartToNative_List(List input) => input;
 createCustomUpgrader(Type customElementClass, $this) => $this;
 
 $endif