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

tools/dom/src/dartium_CustomElementSupport.dart

 // Copyright (c) 2014, 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 dart.dom.html;
 
 /// Dartium ElementUpgrader implementation.
 class _VMElementUpgrader implements ElementUpgrader {
   final Type _type;
   final Type _nativeType;
@@ skipping 35 matching lines @@
       jsObject = unwrap_jso(element);
     } else if (element.runtimeType == js.JsObjectImpl) {
       // It's a Polymer core element (written in JS).
       jsObject = element;
     } else if (isNativeElementExtension) {
       // Extending a native element.
       jsObject = element.blink_jsObject;
 
       // Element to extend is the real tag.
       tag = element.localName;
-    } else if (tag != null && element.localName != tag) { 
+    } else if (tag != null && element.localName != tag) {
       throw new UnsupportedError('Element is incorrect type. Got ${element.runtimeType}, expected native Html or Svg element to extend.');
     } else if (tag == null) {
       throw new UnsupportedError('Element is incorrect type. Got ${element.runtimeType}, expected HtmlElement/JsObjectImpl.');
     }
 
     // Remember Dart class to tagName for any upgrading done in wrap_jso.
-    _addCustomElementType(tag, _type, _extendsTag);
+    addCustomElementType(tag, _type, _extendsTag);
 
-    return createCustomUpgrader(_type, jsObject);
+    return _createCustomUpgrader(_type, jsObject);
   }
 }
 
 /// Validates that the custom type is properly formed-
 ///
 /// * Is a user-defined class.
 /// * Has a created constructor with zero args.
 /// * Derives from an Element subclass.
 ///
 /// Then returns the native base class.
@@ skipping 40 matching lines @@
   return nativeClass;
 }
 
 
 bool _isBuiltinType(ClassMirror cls) {
   // TODO(vsm): Find a less hackish way to do this.
   LibraryMirror lib = cls.owner;
   String libName = lib.uri.toString();
   return libName.startsWith('dart:');
 }