Oilpan: DatabaseThread::m_thread should not get destructed during sweeping

Source/modules/webdatabase/DatabaseContext.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2011 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
@@ skipping 160 matching lines @@
     // stopDatabases(), we can't clear the m_databaseThread ref till we get to
     // the destructor. This is because the Databases that are managed by
     // DatabaseThread still rely on this ref between the context and the thread
     // to execute the task for closing the database. By the time we get to the
     // destructor, we're guaranteed that the databases are destructed (which is
     // why our ref count is 0 then and we're destructing). Then, the
     // m_databaseThread RefPtr destructor will deref and delete the
     // DatabaseThread.
 
     if (m_databaseThread && !m_hasRequestedTermination) {
-        TaskSynchronizer sync;
-        m_databaseThread->requestTermination(&sync);
+        // This blocks until the database thread finishes processing the cleanup task.
+        m_databaseThread->terminate();
         m_hasRequestedTermination = true;
-        sync.waitForTaskCompletion();
     }
 }
 
 bool DatabaseContext::allowDatabaseAccess() const
 {
     return toDocument(executionContext())->isActive();
 }
 
 SecurityOrigin* DatabaseContext::securityOrigin() const
 {
     return executionContext()->securityOrigin();
 }
 
 bool DatabaseContext::isContextThread() const
 {
     return executionContext()->isContextThread();
 }
 
 } // namespace blink