Pass more const RenderObject& in the vicinity of paint-servers

Source/core/rendering/svg/RenderSVGResourceGradient.h

 /*
  * Copyright (C) 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2008 Eric Seidel <eric@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
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 29 matching lines @@
 
 class GraphicsContext;
 
 class RenderSVGResourceGradient : public RenderSVGResourceContainer {
 public:
     explicit RenderSVGResourceGradient(SVGGradientElement*);
 
     virtual void removeAllClientsFromCache(bool markForInvalidation = true) override final;
     virtual void removeClientFromCache(RenderObject*, bool markForInvalidation = true) override final;
 
-    virtual SVGPaintServer preparePaintServer(RenderObject*) override final;
+    virtual SVGPaintServer preparePaintServer(const RenderObject&) override final;
 
     virtual bool isChildAllowed(RenderObject* child, RenderStyle*) const override final;
 
 protected:
     void addStops(GradientData*, const Vector<Gradient::ColorStop>&) const;
 
     virtual SVGUnitTypes::SVGUnitType gradientUnits() const = 0;
     virtual void calculateGradientTransform(AffineTransform&) = 0;
     virtual bool collectGradientAttributes(SVGGradientElement*) = 0;
     virtual void buildGradient(GradientData*) const = 0;
 
     GradientSpreadMethod platformSpreadMethodFromSVGType(SVGSpreadMethodType) const;
 
 private:
     bool m_shouldCollectGradientAttributes : 1;
-    HashMap<RenderObject*, OwnPtr<GradientData> > m_gradientMap;
+    HashMap<const RenderObject*, OwnPtr<GradientData> > m_gradientMap;
 };
 
 }
 
 #endif