[oilpan]: Remove support for tracing off-heap hashmaps.

Source/core/timing/PerformanceUserTiming.cpp

 /*
  * Copyright (C) 2012 Intel 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 189 matching lines @@
     return convertToEntrySequence(m_measuresMap);
 }
 
 PerformanceEntryVector UserTiming::getMeasures(const String& name) const
 {
     return getEntrySequenceByName(m_measuresMap, name);
 }
 
 void UserTiming::trace(Visitor* visitor)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_performance);
     visitor->trace(m_marksMap);
     visitor->trace(m_measuresMap);
+#endif
 }
 
 } // namespace blink