Turn WorkerLoaderProxy into a threadsafe, ref-counted object.

Source/core/workers/DedicatedWorkerThread.h

Index: Source/core/workers/DedicatedWorkerThread.h
diff --git a/Source/core/workers/DedicatedWorkerThread.h b/Source/core/workers/DedicatedWorkerThread.h
index 5f03f26f9edca069c8ffaf32416b13ac1a712f89..ac6fa4b2cae44089d32d3f16d0ddbe4c5e5f5240 100644
--- a/Source/core/workers/DedicatedWorkerThread.h
+++ b/Source/core/workers/DedicatedWorkerThread.h
@@ -40,7 +40,7 @@ class WorkerThreadStartupData;
 
 class DedicatedWorkerThread final : public WorkerThread {
 public:
-    static PassRefPtr<DedicatedWorkerThread> create(WorkerLoaderProxy&, WorkerObjectProxy&, double timeOrigin, PassOwnPtrWillBeRawPtr<WorkerThreadStartupData>);
+    static PassRefPtr<DedicatedWorkerThread> create(PassRefPtr<WorkerLoaderProxy>, WorkerObjectProxy&, double timeOrigin, PassOwnPtrWillBeRawPtr<WorkerThreadStartupData>);
     WorkerObjectProxy& workerObjectProxy() const { return m_workerObjectProxy; }
     virtual ~DedicatedWorkerThread();
 
@@ -49,7 +49,7 @@ protected:
     virtual void postInitialize() override;
 
 private:
-    DedicatedWorkerThread(WorkerLoaderProxy&, WorkerObjectProxy&, double timeOrigin, PassOwnPtrWillBeRawPtr<WorkerThreadStartupData>);
+    DedicatedWorkerThread(PassRefPtr<WorkerLoaderProxy>, WorkerObjectProxy&, double timeOrigin, PassOwnPtrWillBeRawPtr<WorkerThreadStartupData>);
 
     WorkerObjectProxy& m_workerObjectProxy;
     double m_timeOrigin;