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

Source/core/svg/animation/SVGSMILElement.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 153 matching lines @@
     , m_beginOrEnd(beginOrEnd)
     , m_baseID(baseID)
     , m_name(name)
     , m_offset(offset)
     , m_repeat(repeat)
 {
 }
 
 SVGSMILElement::SVGSMILElement(const QualifiedName& tagName, Document& doc)
     : SVGElement(tagName, doc)
-    , SVGTests(this)
     , m_attributeName(anyQName())
     , m_targetElement(nullptr)
     , m_syncBaseConditionsConnected(false)
     , m_hasEndEventConditions(false)
     , m_isWaitingForFirstInterval(true)
     , m_interval(SMILInterval(SMILTime::unresolved(), SMILTime::unresolved()))
     , m_previousIntervalBegin(SMILTime::unresolved())
     , m_activeState(Inactive)
     , m_lastPercent(0)
     , m_lastRepeat(0)
     , m_nextProgressTime(0)
     , m_documentOrderIndex(0)
     , m_cachedDur(invalidCachedTime)
     , m_cachedRepeatDur(invalidCachedTime)
     , m_cachedRepeatCount(invalidCachedTime)
     , m_cachedMin(invalidCachedTime)
     , m_cachedMax(invalidCachedTime)
 {
+    SVGTests::initialize(this);
+
     resolveFirstInterval();
 }
 
 SVGSMILElement::~SVGSMILElement()
 {
 #if !ENABLE(OILPAN)
     clearResourceAndEventBaseReferences();
 #endif
     smilEndEventSender().cancelEvent(this);
     smilBeginEventSender().cancelEvent(this);
@@ skipping 1157 matching lines @@
     visitor->trace(m_targetElement);
     visitor->trace(m_timeContainer);
     visitor->trace(m_conditions);
     visitor->trace(m_syncBaseDependents);
 #endif
     SVGElement::trace(visitor);
     SVGTests::trace(visitor);
 }
 
 } // namespace blink