Introduce DEFINE_RENDER_OBJECT_TYPE_CASTS to replace manual toRenderFoo, and use it

Source/core/rendering/svg/RenderSVGGradientStop.h

 /*
  * Copyright (C) 2007 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Google, Inc.
  *
  * 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 36 matching lines @@
     virtual FloatRect strokeBoundingBox() const { return FloatRect(); }
     virtual FloatRect repaintRectInLocalCoordinates() const { return FloatRect(); }
 
 protected:
     virtual void styleDidChange(StyleDifference, const RenderStyle* oldStyle);
 
 private:
     SVGGradientElement* gradientElement() const;
 };
 
-inline const RenderSVGGradientStop* toRenderSVGGradientStop(const RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isSVGGradientStop());
-    return static_cast<const RenderSVGGradientStop*>(object);
-}
+DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderSVGGradientStop, isSVGGradientStop());
 
 }
 
 #endif // RenderSVGGradientStop_h