Introduce isHTMLLabelElement and toHTMLLabelElement

Source/core/html/HTMLLabelElement.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 37 matching lines @@
     // Overridden to update the hover/active state of the corresponding control.
     virtual void setActive(bool = true, bool pause = false);
     virtual void setHovered(bool = true);
 
     // Overridden to either click() or focus() the corresponding control.
     virtual void defaultEventHandler(Event*);
 
     virtual void focus(bool restorePreviousSelection, FocusDirection) OVERRIDE;
 };
 
+inline bool isHTMLLabelElement(const Node* node)
+{
+    return node->hasTagName(HTMLNames::labelTag);
+}
+
+inline bool isHTMLLabelElement(const Element* element)
+{
+    return element->hasTagName(HTMLNames::labelTag);
+}
+
+inline HTMLLabelElement* toHTMLLabelElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || isHTMLLabelElement(node));
+    return static_cast<HTMLLabelElement*>(node);
+}
+
 } //namespace
 
 #endif