Drop SVGElement::isSVGSVGElement() virtual function

Source/core/svg/SVGLengthContext.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2007 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. 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 290 matching lines @@
     }
 
     // Root <svg> element lengths are resolved against the top level viewport.
     if (m_context->isOutermostSVGSVGElement()) {
         viewportSize = toSVGSVGElement(m_context)->currentViewportSize();
         return true;
     }
 
     // Take size from nearest viewport element.
     SVGElement* viewportElement = m_context->viewportElement();
-    if (!viewportElement || !viewportElement->isSVGSVGElement())
+    if (!isSVGSVGElement(viewportElement))
         return false;
 
-    const SVGSVGElement* svg = toSVGSVGElement(viewportElement);
-    viewportSize = svg->currentViewBoxRect().size();
+    const SVGSVGElement& svg = toSVGSVGElement(*viewportElement);
+    viewportSize = svg.currentViewBoxRect().size();
     if (viewportSize.isEmpty())
-        viewportSize = svg->currentViewportSize();
+        viewportSize = svg.currentViewportSize();
 
     return true;
 }
 
 }