Remove support for the externalResourcesRequired attribute.

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 69 matching lines @@
     SVGSVGElement* ownerSVGElement() const;
     SVGElement* viewportElement() const;
 
     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 isStructurallyExternal() const { return false; }
 
     // For SVGTests
     virtual bool isValid() const { return true; }
 
     virtual void svgAttributeChanged(const QualifiedName&);
 
     virtual void animatedPropertyTypeForAttribute(const QualifiedName&, Vector<AnimatedPropertyType>&);
     PassRefPtr<NewSVGAnimatedPropertyBase> propertyFromAttribute(const QualifiedName& attributeName);
 
     void sendSVGLoadEventIfPossible(bool sendParentLoadEvents = false);
@@ skipping 149 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