Fix DOMWindow::isCurrentlyDisplayedInFrame to return false when detached

Source/core/frame/BarProp.cpp

 /*
  * Copyright (C) 2007, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 26 matching lines @@
 
 BarProp::BarProp(LocalFrame* frame, Type type)
     : DOMWindowProperty(frame)
     , m_type(type)
 {
     ScriptWrappable::init(this);
 }
 
 bool BarProp::visible() const
 {
-    ASSERT(m_frame);
     if (!m_frame)
         return false;
     FrameHost* host = m_frame->host();
     if (!host)
         return false;
 
     switch (m_type) {
     case Locationbar:
     case Personalbar:
     case Toolbar:
         return host->chrome().toolbarsVisible();
     case Menubar:
         return host->chrome().menubarVisible();
     case Scrollbars:
         return host->chrome().scrollbarsVisible();
     case Statusbar:
         return host->chrome().statusbarVisible();
     }
 
     ASSERT_NOT_REACHED();
     return false;
 }
 
 } // namespace WebCore