Have Document::accessSVGExtensions() return a reference

Source/core/svg/SVGElement.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  * Copyright (C) 2009 Apple Inc. 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 63 matching lines @@
 
     const AtomicString& xmllang() const;
     void setXMLlang(const AtomicString&);
 
     const AtomicString& xmlspace() const;
     void setXMLspace(const AtomicString&);
 
     SVGSVGElement* ownerSVGElement() const;
     SVGElement* viewportElement() const;
 
-    SVGDocumentExtensions* accessDocumentSVGExtensions();
+    SVGDocumentExtensions& accessDocumentSVGExtensions();
 
     virtual bool isSVGGraphicsElement() const { return false; }
     virtual bool isSVGSVGElement() const { return false; }
     virtual bool isFilterEffect() const { return false; }
     virtual bool isGradientStop() const { return false; }
     virtual bool isTextContent() const { return false; }
     virtual bool isTextPositioning() const { return false; }
     virtual bool isStructurallyExternal() const { return false; }
 
     // For SVGTests
@@ skipping 159 matching lines @@
         return DefaultHash<QualifiedName>::Hash::hash(key);
     }
     static bool equal(const QualifiedName& a, const QualifiedName& b) { return a.matches(b); }
 };
 
 DEFINE_NODE_TYPE_CASTS(SVGElement, isSVGElement());
 
 }
 
 #endif