Simplify SVGSMILElement::notifyDependentsIntervalChanged loop breaker.

third_party/WebKit/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 1204 matching lines @@
 
     m_nextProgressTime = calculateNextProgressTime(elapsed);
     return animationIsContributing;
 }
 
 void SVGSMILElement::notifyDependentsIntervalChanged()
 {
     ASSERT(m_interval.begin.isFinite());
     // |loopBreaker| is used to avoid infinite recursions which may be caused from:
     // |notifyDependentsIntervalChanged| -> |createInstanceTimesFromSyncbase| -> |add{Begin,End}Time| -> |{begin,end}TimeChanged| -> |notifyDependentsIntervalChanged|
-    // |loopBreaker| is defined as a Persistent<HeapHashSet<Member<SVGSMILElement>>>. This won't cause leaks because it is guaranteed to be empty after the root |notifyDependentsIntervalChanged| has exited.
-    DEFINE_STATIC_LOCAL(HeapHashSet<Member<SVGSMILElement>>, loopBreaker, (new HeapHashSet<Member<SVGSMILElement>>));
+    //
+    // As the set here records SVGSMILElements on the stack, it is acceptable to
+    // use a HashSet of untraced heap references -- any conservative GC which
+    // strikes before unwinding will find these elements on the stack.
+    DEFINE_STATIC_LOCAL(HashSet<UntracedMember<SVGSMILElement>>, loopBreaker, ());
     if (!loopBreaker.add(this).isNewEntry)
         return;
 
     for (SVGSMILElement* element : m_syncBaseDependents)
         element->createInstanceTimesFromSyncbase(this);
 
     loopBreaker.remove(this);
 }
 
 void SVGSMILElement::createInstanceTimesFromSyncbase(SVGSMILElement* syncBase)
@@ skipping 119 matching lines @@
 {
     visitor->trace(m_targetElement);
     visitor->trace(m_timeContainer);
     visitor->trace(m_conditions);
     visitor->trace(m_syncBaseDependents);
     SVGElement::trace(visitor);
     SVGTests::trace(visitor);
 }
 
 } // namespace blink