Introduce toSVGRadialGradientElement(), and use it

Source/core/rendering/svg/RenderSVGResourceRadialGradient.cpp

 /*
  * Copyright (C) 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2012 Adobe Systems Incorporated. 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 24 matching lines @@
 {
 }
 
 RenderSVGResourceRadialGradient::~RenderSVGResourceRadialGradient()
 {
 }
 
 bool RenderSVGResourceRadialGradient::collectGradientAttributes(SVGGradientElement* gradientElement)
 {
     m_attributes = RadialGradientAttributes();
-    return static_cast<SVGRadialGradientElement*>(gradientElement)->collectGradientAttributes(m_attributes);
+    return toSVGRadialGradientElement(gradientElement)->collectGradientAttributes(m_attributes);
 }
 
 FloatPoint RenderSVGResourceRadialGradient::centerPoint(const RadialGradientAttributes& attributes) const
 {
     return SVGLengthContext::resolvePoint(static_cast<const SVGElement*>(node()), attributes.gradientUnits(), attributes.cx(), attributes.cy());
 }
 
 FloatPoint RenderSVGResourceRadialGradient::focalPoint(const RadialGradientAttributes& attributes) const
 {
     return SVGLengthContext::resolvePoint(static_cast<const SVGElement*>(node()), attributes.gradientUnits(), attributes.fx(), attributes.fy());
@@ skipping 15 matching lines @@
         this->focalRadius(m_attributes),
         this->centerPoint(m_attributes),
         this->radius(m_attributes));
 
     gradientData->gradient->setSpreadMethod(platformSpreadMethodFromSVGType(m_attributes.spreadMethod()));
 
     addStops(gradientData, m_attributes.stops());
 }
 
 }