Add toSVGCircleElement(), 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 59 matching lines @@
     m_fillBoundingBox = FloatRect(m_center.x() - m_radii.width(), m_center.y() - m_radii.height(), 2 * m_radii.width(), 2 * m_radii.height());
     m_strokeBoundingBox = m_fillBoundingBox;
     if (style()->svgStyle()->hasStroke())
         m_strokeBoundingBox.inflate(strokeWidth() / 2);
 }
 
 void RenderSVGEllipse::calculateRadiiAndCenter()
 {
     ASSERT(node());
     if (node()->hasTagName(SVGNames::circleTag)) {
-
-        SVGCircleElement* circle = static_cast<SVGCircleElement*>(node());
+        SVGCircleElement* circle = toSVGCircleElement(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());
@@ skipping 56 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;
 }
 
 }