Add toSVGGlyphRefElement(), and use it as much as possible

Source/core/svg/SVGGlyphRefElement.h

 /*
  * Copyright (C) 2011 Leo Yang <leoyang@webkit.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 SVGGlyphRefElement_h
 #define SVGGlyphRefElement_h
 
 #if ENABLE(SVG_FONTS)
+#include "SVGNames.h"
 #include "core/svg/SVGElement.h"
 #include "core/svg/SVGURIReference.h"
 
 namespace WebCore {
 
 class SVGGlyphRefElement FINAL : public SVGElement,
                                  public SVGURIReference {
 public:
     static PassRefPtr<SVGGlyphRefElement> create(const QualifiedName&, Document&);
 
@@ skipping 23 matching lines @@
     BEGIN_DECLARE_ANIMATED_PROPERTIES(SVGGlyphRefElement)
         DECLARE_ANIMATED_STRING(Href, href)
     END_DECLARE_ANIMATED_PROPERTIES
 
     float m_x;
     float m_y;
     float m_dx;
     float m_dy;
 };
 
+inline SVGGlyphRefElement* toSVGGlyphRefElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::glyphRefTag));
+    return static_cast<SVGGlyphRefElement*>(node);
+}
+
 }
 
 #endif
 #endif