Hide internal methods like wrap_jso from the dart:html public interface

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 376 matching lines @@
       // Only components derived from HTML* can be extended.
       throw new DomException.jsInterop("HierarchyRequestError: Only HTML elements can be customized.");
     }
 
     var customClassType = _getDartHtmlClassName(classMirror);
 
     if (extendsTag != null) {
       var nativeElement = document.createElement(extendsTag);
 
       // Trying to extend a native element is it the Dart class consistent with the
-      // extendsTag? 
+      // extendsTag?
       if (nativeElement.runtimeType != customClassType.reflectedType) {
         var nativeElementClassMirror = reflectClass(nativeElement.runtimeType);
         var customClassNativeElement = MirrorSystem.getName(customClassType.simpleName);
         var extendsNativeElement = MirrorSystem.getName(nativeElementClassMirror.simpleName);
         throw new DomException.jsInterop("HierarchyRequestError: Custom class type ($customClassNativeElement) and extendsTag class ($extendsNativeElement) don't match .");
       }
     } else if (customClassType.reflectedType != HtmlElement && customClassType.reflectedType != svg.SvgElement) {
       var customClassName = MirrorSystem.getName(classMirror.simpleName);
       var customClassElement = MirrorSystem.getName(customClassType.simpleName);
       throw new DomException.jsInterop("HierarchyRequestError: Custom element $customClassName is a native $customClassElement should be derived from HtmlElement or SvgElement.");
     }
 
     if (_hasCreatedConstructor(classMirror)) {
       // Start the hookup the JS way create an <x-foo> element that extends the
       // <x-base> custom element. Inherit its prototype and signal what tag is
       // inherited:
       //
       //     var myProto = Object.create(HTMLElement.prototype);
       //     var myElement = document.registerElement('x-foo', {prototype: myProto});
       var baseElement = js.JsNative.getProperty(js.context, jsClassName);
       if (baseElement == null) {
         // Couldn't find the HTML element so use a generic one.
         baseElement = js.JsNative.getProperty(js.context, 'HTMLElement');
       }
       var elemProto = js.JsNative.callMethod(js.JsNative.getProperty(js.context, 'Object'), "create", [js.JsNative.getProperty(baseElement, 'prototype')]);
 
       // Remember for any upgrading done in wrap_jso.
-      _addCustomElementType(tag, customElementClass, extendsTag);
+      addCustomElementType(tag, customElementClass, extendsTag);
 
       // TODO(terry): Hack to stop recursion re-creating custom element when the
       //              created() constructor of the custom element does e.g.,
       //
       //                  MyElement.created() : super.created() {
       //                    this.innerHtml = "<b>I'm an x-foo-with-markup!</b>";
       //                  }
       //
       //              sanitizing causes custom element to created recursively
       //              until stack overflow.
@@ skipping 112 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
   }
 }