:hover style not applied on hover if its display property is different from original style's

Source/core/html/HTMLOptGroupElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 29 matching lines @@
     String groupLabelText() const;
 
 private:
     HTMLOptGroupElement(const QualifiedName&, Document*);
 
     virtual const AtomicString& formControlType() const;
     virtual bool supportsFocus() const;
     virtual bool isFocusable() const;
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) OVERRIDE;
     virtual bool rendererIsNeeded(const NodeRenderingContext&) { return false; }
-    virtual void attach();
-    virtual void detach();
+    virtual void attach(const AttachContext& = AttachContext()) OVERRIDE;
+    virtual void detach(const AttachContext& = AttachContext()) OVERRIDE;
 
     virtual void childrenChanged(bool changedByParser = false, Node* beforeChange = 0, Node* afterChange = 0, int childCountDelta = 0);
 
     virtual void accessKeyAction(bool sendMouseEvents);
 
     // <optgroup> never has a renderer so we manually manage a cached style.
     void updateNonRenderStyle();
     virtual RenderStyle* nonRendererStyle() const OVERRIDE;
     virtual PassRefPtr<RenderStyle> customStyleForRenderer() OVERRIDE;
 
     void recalcSelectOptions();
 
     RefPtr<RenderStyle> m_style;
 };
 
 } //namespace
 
 #endif