Use toSVGMarkerElement() instead of static_cast<>

Source/core/rendering/svg/RenderSVGResourceMarker.h

 /*
  * Copyright (C) Research In Motion Limited 2009-2010. 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 41 matching lines @@
     virtual void calcViewport();
 
     virtual const AffineTransform& localToParentTransform() const;
     AffineTransform markerTransformation(const FloatPoint& origin, float angle, float strokeWidth) const;
 
     virtual bool applyResource(RenderObject*, RenderStyle*, GraphicsContext*&, unsigned short) { return false; }
     virtual FloatRect resourceBoundingBox(RenderObject*) { return FloatRect(); }
 
     FloatPoint referencePoint() const;
     float angle() const;
-    SVGMarkerUnitsType markerUnits() const { return static_cast<SVGMarkerElement*>(node())->markerUnitsCurrentValue(); }
+    SVGMarkerUnitsType markerUnits() const { return toSVGMarkerElement(node())->markerUnitsCurrentValue(); }
 
     virtual RenderSVGResourceType resourceType() const { return s_resourceType; }
     static RenderSVGResourceType s_resourceType;
 
 private:
     // Generates a transformation matrix usable to render marker content. Handles scaling the marker content
     // acording to SVGs markerUnits="strokeWidth" concept, when a strokeWidth value != -1 is passed in.
     AffineTransform markerContentTransformation(const AffineTransform& contentTransformation, const FloatPoint& origin, float strokeWidth = -1) const;
 
     AffineTransform viewportTransform() const;
 
     mutable AffineTransform m_localToParentTransform;
     FloatRect m_viewport;
 };
 
 }
 
 #endif