[Oilpan] Apply RefCountedGarbageCollectedEventTarget on AbstractWorker

Source/core/workers/WorkerMessagingProxy.cpp

Index: Source/core/workers/WorkerMessagingProxy.cpp
diff --git a/Source/core/workers/WorkerMessagingProxy.cpp b/Source/core/workers/WorkerMessagingProxy.cpp
index 228b63f2c06ab3701369fcccec7e8befc0ea8e05..284b6cec7f61cd1e07058b2d9e3622082873eb6f 100644
--- a/Source/core/workers/WorkerMessagingProxy.cpp
+++ b/Source/core/workers/WorkerMessagingProxy.cpp
@@ -202,7 +202,6 @@ void WorkerMessagingProxy::workerThreadCreated(PassRefPtr<WorkerThread> workerTh
 
 void WorkerMessagingProxy::workerObjectDestroyed()
 {
-    m_workerObject = nullptr;

[sof, 2015/08/13 20:44:01]

Why is clearing this promptly redundant now - can you guarantee that the posted
task from workerObjectDestroyed() won't touch m_workerObject somehow? (it seems
tidier overall to clear it to make the worker object detachment obvious.)

[haraken, 2015/08/13 23:53:03]

workerObjectDestroyed() is called in InProcessWorkerBase's destructor. Thus it
is guaranteed that m_workerObject is already cleared when the
workerObjectDestroyed() gets called.

Maybe worth having ASSERT(!m_workerObject).

[peria, 2015/08/14 03:43:41]

Done.

     m_executionContext->postTask(FROM_HERE, createCrossThreadTask(&WorkerMessagingProxy::workerObjectDestroyedInternal, this));
 }