Introduce isHTMLOptGroupElement and toHTMLOptGroupElement

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 45 matching lines @@
     // <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;
 };
 
+inline bool isHTMLOptGroupElement(const Node* node)
+{
+    return node->hasTagName(HTMLNames::optgroupTag);
+}
+
+inline bool isHTMLOptGroupElement(const Element* element)
+{
+    return element->hasTagName(HTMLNames::optgroupTag);
+}
+
+inline HTMLOptGroupElement* toHTMLOptGroupElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || isHTMLOptGroupElement(node));
+    return static_cast<HTMLOptGroupElement*>(node);
+}
+
 } //namespace
 
 #endif