Introduce toSVGEllipseElement(), and use it

Source/core/rendering/svg/RenderSVGEllipse.cpp

 /*
  * Copyright (C) 2012 Google, Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 69 matching lines @@
 
         SVGCircleElement* circle = static_cast<SVGCircleElement*>(node());
 
         SVGLengthContext lengthContext(circle);
         float radius = circle->rCurrentValue().value(lengthContext);
         m_radii = FloatSize(radius, radius);
         m_center = FloatPoint(circle->cxCurrentValue().value(lengthContext), circle->cyCurrentValue().value(lengthContext));
         return;
     }
 
-    ASSERT(node()->hasTagName(SVGNames::ellipseTag));
-    SVGEllipseElement* ellipse = static_cast<SVGEllipseElement*>(node());
+    SVGEllipseElement* ellipse = toSVGEllipseElement(node());
 
     SVGLengthContext lengthContext(ellipse);
     m_radii = FloatSize(ellipse->rxCurrentValue().value(lengthContext), ellipse->ryCurrentValue().value(lengthContext));
     m_center = FloatPoint(ellipse->cxCurrentValue().value(lengthContext), ellipse->cyCurrentValue().value(lengthContext));
 }
 
 void RenderSVGEllipse::fillShape(GraphicsContext* context) const
 {
     if (m_usePathFallback) {
         RenderSVGShape::fillShape(context);
@@ skipping 46 matching lines @@
     FloatPoint center = FloatPoint(m_center.x() - point.x(), m_center.y() - point.y());
 
     // This works by checking if the point satisfies the ellipse equation.
     // (x/rX)^2 + (y/rY)^2 <= 1
     float xrX = center.x() / m_radii.width();
     float yrY = center.y() / m_radii.height();
     return xrX * xrX + yrY * yrY <= 1.0;
 }
 
 }