[Oilpan] Apply RefCountedGarbageCollectedEventTarget on AbstractWorker

Source/core/workers/Worker.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef Worker_h
 #define Worker_h
 
 #include "core/workers/InProcessWorkerBase.h"
 
 namespace blink {
 
 class ExceptionState;
 class ExecutionContext;
 class WorkerGlobalScopeProxy;
 
 class CORE_EXPORT Worker final : public InProcessWorkerBase {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    static PassRefPtrWillBeRawPtr<Worker> create(ExecutionContext*, const String& url, ExceptionState&);
+    static Worker* create(ExecutionContext*, const String& url, ExceptionState&);
     ~Worker() override;
 
 protected:
     explicit Worker(ExecutionContext*);
 
     WorkerGlobalScopeProxy* createWorkerGlobalScopeProxy(ExecutionContext*) override;
     const AtomicString& interfaceName() const override;
 };
 
 } // namespace blink
 
 #endif // Worker_h