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

Source/core/svg/SVGSymbolElement.cpp

 /*
  * Copyright (C) 2004, 2005 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 11 matching lines @@
 
 #include "core/svg/SVGSymbolElement.h"
 
 #include "core/SVGNames.h"
 #include "core/rendering/svg/RenderSVGHiddenContainer.h"
 
 namespace blink {
 
 inline SVGSymbolElement::SVGSymbolElement(Document& document)
     : SVGElement(SVGNames::symbolTag, document)
-    , SVGFitToViewBox(this)
 {
+    SVGFitToViewBox::initialize(this);
 }
 
 void SVGSymbolElement::trace(Visitor* visitor)
 {
     SVGElement::trace(visitor);
     SVGFitToViewBox::trace(visitor);
 }
 
 DEFINE_NODE_FACTORY(SVGSymbolElement)
 
 void SVGSymbolElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
     parseAttributeNew(name, value);
 }
 
 void SVGSymbolElement::svgAttributeChanged(const QualifiedName& attrName)
 {
     if (SVGFitToViewBox::isKnownAttribute(attrName))
         invalidateInstances();
 }
 
 RenderObject* SVGSymbolElement::createRenderer(RenderStyle*)
 {
     return new RenderSVGHiddenContainer(this);
 }
 
 }