ServiceWorker: Fix data race in shutdown sequence

Source/web/WebEmbeddedWorkerImpl.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 153 matching lines @@
     , m_mainFrame(0)
     , m_askedToTerminate(false)
     , m_pauseAfterDownloadState(DontPauseAfterDownload)
     , m_waitingForDebuggerState(NotWaitingForDebugger)
 {
     runningWorkerInstances().add(this);
 }
 
 WebEmbeddedWorkerImpl::~WebEmbeddedWorkerImpl()
 {
+    if (m_workerThread)
+        m_workerThread->terminateAndWait();
+
     ASSERT(runningWorkerInstances().contains(this));
     runningWorkerInstances().remove(this);
     ASSERT(m_webView);
 
     // Detach the client before closing the view to avoid getting called back.
     toWebLocalFrameImpl(m_mainFrame)->setClient(0);
 
     m_webView->close();
     m_mainFrame->close();
 }
@@ skipping 236 matching lines @@
     m_mainScriptLoader.clear();
 
     m_workerGlobalScopeProxy = ServiceWorkerGlobalScopeProxy::create(*this, *document, *m_workerContextClient);
     m_loaderProxy = LoaderProxy::create(*this);
     m_workerThread = ServiceWorkerThread::create(*m_loaderProxy, *m_workerGlobalScopeProxy, startupData.release());
     m_workerThread->start();
     m_workerInspectorProxy->workerThreadCreated(document, m_workerThread.get(), scriptURL);
 }
 
 } // namespace blink