Initialize GC mixin bases only when leftmost vtable has been initialized.

Source/core/svg/SVGImageElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Rob Buis <buis@kde.org>
  * Copyright (C) 2006 Alexander Kellett <lypanov@kde.org>
  *
  * 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 14 matching lines @@
 
 #include "core/CSSPropertyNames.h"
 #include "core/XLinkNames.h"
 #include "core/rendering/RenderImageResource.h"
 #include "core/rendering/svg/RenderSVGImage.h"
 
 namespace blink {
 
 inline SVGImageElement::SVGImageElement(Document& document)
     : SVGGraphicsElement(SVGNames::imageTag, document)
-    , SVGURIReference(this)
     , m_x(SVGAnimatedLength::create(this, SVGNames::xAttr, SVGLength::create(LengthModeWidth), AllowNegativeLengths))
     , m_y(SVGAnimatedLength::create(this, SVGNames::yAttr, SVGLength::create(LengthModeHeight), AllowNegativeLengths))
     , m_width(SVGAnimatedLength::create(this, SVGNames::widthAttr, SVGLength::create(LengthModeWidth), ForbidNegativeLengths))
     , m_height(SVGAnimatedLength::create(this, SVGNames::heightAttr, SVGLength::create(LengthModeHeight), ForbidNegativeLengths))
     , m_preserveAspectRatio(SVGAnimatedPreserveAspectRatio::create(this, SVGNames::preserveAspectRatioAttr, SVGPreserveAspectRatio::create()))
     , m_imageLoader(SVGImageLoader::create(this))
     , m_needsLoaderURIUpdate(true)
 {
+    SVGURIReference::initialize(this);
+
     addToPropertyMap(m_x);
     addToPropertyMap(m_y);
     addToPropertyMap(m_width);
     addToPropertyMap(m_height);
     addToPropertyMap(m_preserveAspectRatio);
 }
 
 DEFINE_NODE_FACTORY(SVGImageElement)
 
 void SVGImageElement::trace(Visitor* visitor)
@@ skipping 155 matching lines @@
     return AtomicString(hrefString());
 }
 
 void SVGImageElement::didMoveToNewDocument(Document& oldDocument)
 {
     imageLoader().elementDidMoveToNewDocument();
     SVGGraphicsElement::didMoveToNewDocument(oldDocument);
 }
 
 } // namespace blink