Introduce toSVGPolygonElement(), and use it

Source/core/svg/SVGPolygonElement.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef SVGPolygonElement_h
 #define SVGPolygonElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGPolyElement.h"
 
 namespace WebCore {
 
 class SVGPolygonElement FINAL : public SVGPolyElement {
 public:
     static PassRefPtr<SVGPolygonElement> create(const QualifiedName&, Document*);
 
 private:
     SVGPolygonElement(const QualifiedName&, Document*);
 };
 
+inline SVGPolygonElement* toSVGPolygonElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::polygonTag));
+    return static_cast<SVGPolygonElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif