[Oilpan] Apply RefCountedGarbageCollectedEventTarget on AbstractWorker

Source/core/workers/WorkerMessagingProxy.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 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 184 matching lines @@
     m_unconfirmedMessageCount = m_queuedEarlyTasks.size();
     m_workerThreadHadPendingActivity = true; // Worker initialization means a pending activity.
 
     for (auto& earlyTasks : m_queuedEarlyTasks)
         m_workerThread->postTask(FROM_HERE, earlyTasks.release());
     m_queuedEarlyTasks.clear();
 }
 
 void WorkerMessagingProxy::workerObjectDestroyed()
 {
-    m_workerObject = nullptr;
+    // workerObjectDestroyed() is called in InProcessWorkerBase's destructor.
+    // Thus it should be guaranteed that a weak pointer m_workerObject has been cleared
+    // before this method gets called.
+    ASSERT(!m_workerObject);
+
     m_executionContext->postTask(FROM_HERE, createCrossThreadTask(&WorkerMessagingProxy::workerObjectDestroyedInternal, this));
 }
 
 void WorkerMessagingProxy::workerObjectDestroyedInternal()
 {
     m_mayBeDestroyed = true;
     if (m_workerThread)
         terminateWorkerGlobalScope();
     else
         workerThreadTerminated();
@@ skipping 70 matching lines @@
 
     // FIXME: This need to be revisited when we support nested worker one day
     ASSERT(m_executionContext->isDocument());
     Document* document = toDocument(m_executionContext.get());
     LocalFrame* frame = document->frame();
     if (frame)
         frame->console().adoptWorkerMessagesAfterTermination(this);
 }
 
 } // namespace blink