Oilpan: Remove support for tracing off-heap HashSets.

Source/modules/webdatabase/DatabaseThread.cpp

 /*
  * Copyright (C) 2007, 2008, 2013 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
@@ skipping 44 matching lines @@
     // the following clear(). Otherwise, WebThread destructor blocks the caller
     // thread, and causes a deadlock with ThreadState cleanup.
     // DatabaseContext::stop() asks the database thread to close all of
     // databases, and wait until GC heap cleanup of the database thread. So we
     // can safely destruct WebThread here.
     m_thread.clear();
 }
 
 void DatabaseThread::trace(Visitor* visitor)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_openDatabaseSet);
     visitor->trace(m_transactionCoordinator);
+#endif
 }
 
 void DatabaseThread::start()
 {
     if (m_thread)
         return;
     m_thread = adoptPtr(blink::Platform::current()->createThread("WebCore: Database"));
     m_thread->postTask(new Task(WTF::bind(&DatabaseThread::setupDatabaseThread, this)));
 }
 
@@ skipping 86 matching lines @@
 
 void DatabaseThread::scheduleTask(PassOwnPtr<DatabaseTask> task)
 {
     ASSERT(m_thread);
     ASSERT(!task->hasSynchronizer() || task->hasCheckedForTermination());
     // WebThread takes ownership of the task.
     m_thread->postTask(task.leakPtr());
 }
 
 } // namespace WebCore