workers: Move ownership of WebThread from WorkerThread

Source/core/workers/SharedWorkerThread.cpp

Index: Source/core/workers/SharedWorkerThread.cpp
diff --git a/Source/core/workers/SharedWorkerThread.cpp b/Source/core/workers/SharedWorkerThread.cpp
index 91b24ea6f7b0de56c2cc974a871ad3f30322b9e6..6a0e9625586ac9e154566244d791e18d3814b721 100644
--- a/Source/core/workers/SharedWorkerThread.cpp
+++ b/Source/core/workers/SharedWorkerThread.cpp
@@ -43,7 +43,7 @@ PassRefPtr<SharedWorkerThread> SharedWorkerThread::create(const String& name, Pa
 }
 
 SharedWorkerThread::SharedWorkerThread(const String& name, PassRefPtr<WorkerLoaderProxy> workerLoaderProxy, WorkerReportingProxy& workerReportingProxy, PassOwnPtr<WorkerThreadStartupData> startupData)
-    : WorkerThread("SharedWorker Thread", workerLoaderProxy, workerReportingProxy, startupData)
+    : WorkerThread(workerLoaderProxy, workerReportingProxy, startupData)
     , m_name(name.isolatedCopy())
 {
 }
@@ -57,4 +57,11 @@ PassRefPtrWillBeRawPtr<WorkerGlobalScope> SharedWorkerThread::createWorkerGlobal
     return SharedWorkerGlobalScope::create(m_name, this, startupData);
 }
 
+WebThreadSupportingGC& SharedWorkerThread::backingThread()
+{
+    if (!m_thread)
+        m_thread = WebThreadSupportingGC::create("SharedWorker Thread");
+    return *m_thread.get();
+}
+
 } // namespace blink