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

Source/core/workers/WorkerEventQueue.cpp

 /*
  * Copyright (C) 2010 Google 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 34 matching lines @@
 {
 }
 
 WorkerEventQueue::~WorkerEventQueue()
 {
     ASSERT(m_eventTaskMap.isEmpty());
 }
 
 void WorkerEventQueue::trace(Visitor* visitor)
 {
-#if ENABLE(OILPAN)
     visitor->trace(m_executionContext);
     visitor->trace(m_eventTaskMap);
-#endif
     EventQueue::trace(visitor);
 }
 
 class WorkerEventQueue::EventDispatcherTask : public ExecutionContextTask {
 public:
     static PassOwnPtr<EventDispatcherTask> create(PassRefPtrWillBeRawPtr<Event> event, WorkerEventQueue* eventQueue)
     {
         return adoptPtr(new EventDispatcherTask(event, eventQueue));
     }
 
@@ skipping 70 matching lines @@
     for (EventTaskMap::iterator it = m_eventTaskMap.begin(); it != m_eventTaskMap.end(); ++it) {
         Event* event = it->key.get();
         EventDispatcherTask* task = it->value;
         InspectorInstrumentation::didRemoveEvent(event->target(), event);
         task->cancel();
     }
     m_eventTaskMap.clear();
 }
 
 }