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

Source/core/svg/SVGFitToViewBox.cpp

 /*
  * Copyright (C) 2004, 2005, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2010 Rob Buis <buis@kde.org>
  * Copyright (C) 2014 Samsung Electronics. 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 48 matching lines @@
         parseError = ParsingAttributeFailedError;
         return;
     }
 
     if (baseValue()->width() < 0 || baseValue()->height() < 0) {
         parseError = NegativeValueForbiddenError;
         baseValue()->setInvalid();
     }
 }
 
-SVGFitToViewBox::SVGFitToViewBox(SVGElement* element, PropertyMapPolicy propertyMapPolicy)
-    : m_viewBox(SVGAnimatedViewBoxRect::create(element))
-    , m_preserveAspectRatio(SVGAnimatedPreserveAspectRatio::create(element, SVGNames::preserveAspectRatioAttr, SVGPreserveAspectRatio::create()))
+SVGFitToViewBox::SVGFitToViewBox()
 {
+}
+
+void SVGFitToViewBox::initialize(SVGElement* element, PropertyMapPolicy propertyMapPolicy)
+{
+    ASSERT(!m_viewBox);
+    ASSERT(!m_preserveAspectRatio);
     ASSERT(element);
+
+    m_viewBox = SVGAnimatedViewBoxRect::create(element);
+    m_preserveAspectRatio = SVGAnimatedPreserveAspectRatio::create(element, SVGNames::preserveAspectRatioAttr, SVGPreserveAspectRatio::create());
+
     if (propertyMapPolicy == PropertyMapPolicyAdd) {
         element->addToPropertyMap(m_viewBox);
         element->addToPropertyMap(m_preserveAspectRatio);
     }
 }
 
 void SVGFitToViewBox::trace(Visitor* visitor)
 {
     visitor->trace(m_viewBox);
     visitor->trace(m_preserveAspectRatio);
@@ skipping 18 matching lines @@
     supportedAttributes.add(SVGNames::preserveAspectRatioAttr);
 }
 
 void SVGFitToViewBox::updateViewBox(const FloatRect& rect)
 {
     ASSERT(m_viewBox);
     m_viewBox->baseValue()->setValue(rect);
 }
 
 }