Introduce toSVGLinearGradientElement(), and use it

Source/core/svg/SVGLinearGradientElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) Research In Motion Limited 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
@@ skipping 130 matching lines @@
             attributes.setGradientTransform(transform);
         }
 
         if (!attributes.hasStops()) {
             const Vector<Gradient::ColorStop>& stops(current->buildStops());
             if (!stops.isEmpty())
                 attributes.setStops(stops);
         }
 
         if (isLinear) {
-            SVGLinearGradientElement* linear = static_cast<SVGLinearGradientElement*>(current);
+            SVGLinearGradientElement* linear = toSVGLinearGradientElement(current);
 
             if (!attributes.hasX1() && current->hasAttribute(SVGNames::x1Attr))
                 attributes.setX1(linear->x1CurrentValue());
 
             if (!attributes.hasY1() && current->hasAttribute(SVGNames::y1Attr))
                 attributes.setY1(linear->y1CurrentValue());
 
             if (!attributes.hasX2() && current->hasAttribute(SVGNames::x2Attr))
                 attributes.setX2(linear->x2CurrentValue());
 
@@ skipping 24 matching lines @@
 
 bool SVGLinearGradientElement::selfHasRelativeLengths() const
 {
     return x1CurrentValue().isRelative()
         || y1CurrentValue().isRelative()
         || x2CurrentValue().isRelative()
         || y2CurrentValue().isRelative();
 }
 
 }