Introduce toSVGUseElement(), use it

Source/core/rendering/svg/RenderSVGTransformableContainer.cpp

 /*
  * Copyright (C) 2004, 2005 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  * Copyright (C) 2009 Google, Inc.
  *
  * 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 28 matching lines @@
 
 bool RenderSVGTransformableContainer::calculateLocalTransform()
 {
     SVGGraphicsElement* element = toSVGGraphicsElement(node());
 
     // If we're either the renderer for a <use> element, or for any <g> element inside the shadow
     // tree, that was created during the use/symbol/svg expansion in SVGUseElement. These containers
     // need to respect the translations induced by their corresponding use elements x/y attributes.
     SVGUseElement* useElement = 0;
     if (element->hasTagName(SVGNames::useTag))
-        useElement = static_cast<SVGUseElement*>(element);
+        useElement = toSVGUseElement(element);
     else if (element->isInShadowTree() && element->hasTagName(SVGNames::gTag)) {
         SVGElement* correspondingElement = element->correspondingElement();
         if (correspondingElement && correspondingElement->hasTagName(SVGNames::useTag))
-            useElement = static_cast<SVGUseElement*>(correspondingElement);
+            useElement = toSVGUseElement(correspondingElement);
     }
 
     if (useElement) {
         SVGLengthContext lengthContext(useElement);
         FloatSize translation(useElement->xCurrentValue().value(lengthContext), useElement->yCurrentValue().value(lengthContext));
         if (translation != m_lastTranslation)
             m_needsTransformUpdate = true;
         m_lastTranslation = translation;
     }
 
     m_didTransformToRootUpdate = m_needsTransformUpdate || SVGRenderSupport::transformToRootChanged(parent());
     if (!m_needsTransformUpdate)
         return false;
 
     m_localTransform = element->animatedLocalTransform();
     m_localTransform.translate(m_lastTranslation.width(), m_lastTranslation.height());
     m_needsTransformUpdate = false;
     return true;
 }
 
 }