Introduce toSVGFEDiffuseLightingElement(), and use it

Source/core/svg/SVGFELightElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  * Copyright (C) 2005 Oliver Hunt <oliver@nerget.com>
  *
  * 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 172 matching lines @@
         || attrName == SVGNames::limitingConeAngleAttr) {
         ContainerNode* parent = parentNode();
         if (!parent)
             return;
 
         RenderObject* renderer = parent->renderer();
         if (!renderer || !renderer->isSVGResourceFilterPrimitive())
             return;
 
         if (parent->hasTagName(SVGNames::feDiffuseLightingTag)) {
-            SVGFEDiffuseLightingElement* diffuseLighting = static_cast<SVGFEDiffuseLightingElement*>(parent);
-            diffuseLighting->lightElementAttributeChanged(this, attrName);
+            toSVGFEDiffuseLightingElement(parent)->lightElementAttributeChanged(this, attrName);
             return;
         } else if (parent->hasTagName(SVGNames::feSpecularLightingTag)) {
             SVGFESpecularLightingElement* specularLighting = static_cast<SVGFESpecularLightingElement*>(parent);
             specularLighting->lightElementAttributeChanged(this, attrName);
             return;
         }
     }
 
     ASSERT_NOT_REACHED();
 }
 
 void SVGFELightElement::childrenChanged(bool changedByParser, Node* beforeChange, Node* afterChange, int childCountDelta)
 {
     SVGElement::childrenChanged(changedByParser, beforeChange, afterChange, childCountDelta);
 
     if (!changedByParser) {
         if (ContainerNode* parent = parentNode()) {
             RenderObject* renderer = parent->renderer();
             if (renderer && renderer->isSVGResourceFilterPrimitive())
                 RenderSVGResource::markForLayoutAndParentResourceInvalidation(renderer);
         }
     }
 }
 
 }