Revert of Revert of Oilpan: Prepare to make ExecutionContext GarbageCollectedMixin.

Source/core/workers/WorkerGlobalScope.h

Index: Source/core/workers/WorkerGlobalScope.h
diff --git a/Source/core/workers/WorkerGlobalScope.h b/Source/core/workers/WorkerGlobalScope.h
index 1d78a51840c35f9e41eca59e4ee77e6a8d1c1afe..fdb20c0531b0d500cf0d24c7a386058b31e3dc8e 100644
--- a/Source/core/workers/WorkerGlobalScope.h
+++ b/Source/core/workers/WorkerGlobalScope.h
@@ -148,8 +148,10 @@
         void addMessageToWorkerConsole(MessageSource, MessageLevel, const String& message, const String& sourceURL, unsigned lineNumber, PassRefPtr<ScriptCallStack>, ScriptState*);
 
     private:
+#if !ENABLE(OILPAN)
         virtual void refExecutionContext() OVERRIDE FINAL { ref(); }
         virtual void derefExecutionContext() OVERRIDE FINAL { deref(); }
+#endif
 
         virtual const KURL& virtualURL() const OVERRIDE FINAL;
         virtual KURL virtualCompleteURL(const String&) const OVERRIDE FINAL;