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

Source/core/svg/SVGURIReference.cpp

 /*
  * Copyright (C) 2004, 2005, 2008 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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #include "config.h"
 #include "core/svg/SVGURIReference.h"
 
 #include "core/XLinkNames.h"
 #include "core/svg/SVGElement.h"
 #include "platform/weborigin/KURL.h"
 
 namespace blink {
 
-SVGURIReference::SVGURIReference(SVGElement* element)
-    : m_href(SVGAnimatedString::create(element, XLinkNames::hrefAttr, SVGString::create()))
+SVGURIReference::SVGURIReference()
 {
+}
+
+void SVGURIReference::initialize(SVGElement* element)
+{
+    ASSERT(!m_href);
     ASSERT(element);
+
+    m_href = SVGAnimatedString::create(element, XLinkNames::hrefAttr, SVGString::create());
     element->addToPropertyMap(m_href);
 }
 
 void SVGURIReference::trace(Visitor* visitor)
 {
     visitor->trace(m_href);
 }
 
 bool SVGURIReference::isKnownAttribute(const QualifiedName& attrName)
 {
@@ skipping 60 matching lines @@
 
     return treeScope.getElementById(id);
 }
 
 void SVGURIReference::addSupportedAttributes(HashSet<QualifiedName>& supportedAttributes)
 {
     supportedAttributes.add(XLinkNames::hrefAttr);
 }
 
 }