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

Source/core/svg/SVGScriptElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2007 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 16 matching lines @@
 #include "core/XLinkNames.h"
 #include "core/dom/Attribute.h"
 #include "core/dom/ScriptLoader.h"
 #include "core/dom/ScriptRunner.h"
 #include "core/events/Event.h"
 
 namespace blink {
 
 inline SVGScriptElement::SVGScriptElement(Document& document, bool wasInsertedByParser, bool alreadyStarted)
     : SVGElement(SVGNames::scriptTag, document)
-    , SVGURIReference(this)
     , m_svgLoadEventTimer(this, &SVGElement::svgLoadEventTimerFired)
     , m_loader(ScriptLoader::create(this, wasInsertedByParser, alreadyStarted))
 {
+    SVGURIReference::initialize(this);
 }
 
 SVGScriptElement::~SVGScriptElement()
 {
 }
 
 PassRefPtrWillBeRawPtr<SVGScriptElement> SVGScriptElement::create(Document& document, bool insertedByParser)
 {
     return adoptRefWillBeNoop(new SVGScriptElement(document, insertedByParser, false));
 }
@@ skipping 128 matching lines @@
 #endif
 
 void SVGScriptElement::trace(Visitor* visitor)
 {
     visitor->trace(m_loader);
     SVGElement::trace(visitor);
     SVGURIReference::trace(visitor);
 }
 
 } // namespace blink