workers: Move ownership of WebThread from WorkerThread

Source/modules/serviceworkers/ServiceWorkerThread.cpp

Index: Source/modules/serviceworkers/ServiceWorkerThread.cpp
diff --git a/Source/modules/serviceworkers/ServiceWorkerThread.cpp b/Source/modules/serviceworkers/ServiceWorkerThread.cpp
index 2ca84dfd202a0974c98419e8ad675a0c43bb1013..3074cde1b37733ab0f6aac4e993708c4c866f32a 100644
--- a/Source/modules/serviceworkers/ServiceWorkerThread.cpp
+++ b/Source/modules/serviceworkers/ServiceWorkerThread.cpp
@@ -43,7 +43,7 @@ PassRefPtr<ServiceWorkerThread> ServiceWorkerThread::create(PassRefPtr<WorkerLoa
 }
 
 ServiceWorkerThread::ServiceWorkerThread(PassRefPtr<WorkerLoaderProxy> workerLoaderProxy, WorkerReportingProxy& workerReportingProxy, PassOwnPtr<WorkerThreadStartupData> startupData)
-    : WorkerThread("ServiceWorker Thread", workerLoaderProxy, workerReportingProxy, startupData)
+    : WorkerThread(workerLoaderProxy, workerReportingProxy, startupData)
 {
 }
 
@@ -56,4 +56,11 @@ PassRefPtrWillBeRawPtr<WorkerGlobalScope> ServiceWorkerThread::createWorkerGloba
     return ServiceWorkerGlobalScope::create(this, startupData);
 }
 
+WebThreadSupportingGC& ServiceWorkerThread::backingThread()
+{
+    if (!m_thread)
+        m_thread = WebThreadSupportingGC::create("ServiceWorker Thread");
+    return *m_thread.get();
+}
+
 } // namespace blink