Introduce toSVGUseElement(), use it

Source/core/rendering/svg/RenderSVGResourceClipper.cpp

 /*
  * Copyright (C) 2004, 2005, 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Rob Buis <buis@kde.org>
  * Copyright (C) Research In Motion Limited 2009-2010. All rights reserved.
  * Copyright (C) 2011 Dirk Schulze <krit@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.
@@ skipping 216 matching lines @@
             frame()->view()->setPaintBehavior(oldBehavior);
             return false;
         }
         RenderStyle* style = renderer->style();
         if (!style || style->display() == NONE || style->visibility() != VISIBLE)
             continue;
 
         WindRule newClipRule = style->svgStyle()->clipRule();
         bool isUseElement = childNode->hasTagName(SVGNames::useTag);
         if (isUseElement) {
-            SVGUseElement* useElement = static_cast<SVGUseElement*>(childNode);
+            SVGUseElement* useElement = toSVGUseElement(childNode);
             renderer = useElement->rendererClipChild();
             if (!renderer)
                 continue;
             if (!useElement->hasAttribute(SVGNames::clip_ruleAttr))
                 newClipRule = renderer->style()->svgStyle()->clipRule();
         }
 
         // Only shapes, paths and texts are allowed for clipping.
         if (!renderer->isSVGShape() && !renderer->isSVGText())
             continue;
@@ skipping 72 matching lines @@
         AffineTransform transform;
         transform.translate(objectBoundingBox.x(), objectBoundingBox.y());
         transform.scaleNonUniform(objectBoundingBox.width(), objectBoundingBox.height());
         return transform.mapRect(m_clipBoundaries);
     }
 
     return m_clipBoundaries;
 }
 
 }