Introduce toSVGMPathElement(), and use it

Source/core/svg/SVGPathElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 266 matching lines @@
 
 void SVGPathElement::invalidateMPathDependencies()
 {
     // <mpath> can only reference <path> but this dependency is not handled in
     // markForLayoutAndParentResourceInvalidation so we update any mpath dependencies manually.
     ASSERT(document());
     if (HashSet<SVGElement*>* dependencies = document()->accessSVGExtensions()->setOfElementsReferencingTarget(this)) {
         HashSet<SVGElement*>::iterator end = dependencies->end();
         for (HashSet<SVGElement*>::iterator it = dependencies->begin(); it != end; ++it) {
             if ((*it)->hasTagName(SVGNames::mpathTag))
-                static_cast<SVGMPathElement*>(*it)->targetPathChanged();
+                toSVGMPathElement(*it)->targetPathChanged();
         }
     }
 }
 
 Node::InsertionNotificationRequest SVGPathElement::insertedInto(ContainerNode* rootParent)
 {
     SVGGraphicsElement::insertedInto(rootParent);
     invalidateMPathDependencies();
     return InsertionDone;
 }
@@ skipping 102 matching lines @@
     return renderer->path().boundingRect();
 }
 
 RenderObject* SVGPathElement::createRenderer(RenderStyle*)
 {
     // By default, any subclass is expected to do path-based drawing
     return new RenderSVGPath(this);
 }
 
 }