IDL: For DOMString? attribute getters, use null string to represent null

Source/core/frame/NavigatorLanguage.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/frame/NavigatorLanguage.h"
 
 #include "platform/Language.h"
 
 namespace WebCore {
 
 NavigatorLanguage::NavigatorLanguage()
     : m_languagesChanged(true)
 {
 }
 
-AtomicString NavigatorLanguage::language(bool& isNull)
+AtomicString NavigatorLanguage::language()
 {
-    isNull = false;
     return defaultLanguage();
 }
 
 bool NavigatorLanguage::hasLanguagesChanged()
 {
     if (!m_languagesChanged)
         return false;
 
     m_languagesChanged = false;
     return true;
 }
 
 void NavigatorLanguage::setLanguagesChanged()
 {
     m_languagesChanged = true;
 }
 
 } // namespace WebCore