Oilpan: Remove support for tracing off-heap HashSets.

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 1325 matching lines @@
 {
 }
 
 void SVGSMILElement::Condition::trace(Visitor* visitor)
 {
     visitor->trace(m_syncBase);
 }
 
 void SVGSMILElement::trace(Visitor* visitor)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_targetElement);
     visitor->trace(m_timeContainer);
     visitor->trace(m_conditions);
     visitor->trace(m_syncBaseDependents);
+#endif
     SVGElement::trace(visitor);
 }
 
 }