Introduce toSVGMPathElement(), and use it

Source/core/svg/SVGAnimateMotionElement.cpp

 /*
  * Copyright (C) 2007 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2008 Apple Inc. 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 119 matching lines @@
     return RotateAngle;
 }
 
 void SVGAnimateMotionElement::updateAnimationPath()
 {
     m_animationPath = Path();
     bool foundMPath = false;
 
     for (Node* child = firstChild(); child; child = child->nextSibling()) {
         if (child->hasTagName(SVGNames::mpathTag)) {
-            SVGMPathElement* mPath = static_cast<SVGMPathElement*>(child);
+            SVGMPathElement* mPath = toSVGMPathElement(child);
             SVGPathElement* pathElement = mPath->pathElement();
             if (pathElement) {
                 updatePathFromGraphicsElement(pathElement, m_animationPath);
                 foundMPath = true;
                 break;
             }
         }
     }
 
     if (!foundMPath && fastHasAttribute(SVGNames::pathAttr))
@@ skipping 190 matching lines @@
 
 void SVGAnimateMotionElement::updateAnimationMode()
 {
     if (!m_animationPath.isEmpty())
         setAnimationMode(PathAnimation);
     else
         SVGAnimationElement::updateAnimationMode();
 }
 
 }