Add blink::WebWaitableEvent interface (blink side)

Source/core/workers/WorkerThread.h

Index: Source/core/workers/WorkerThread.h
diff --git a/Source/core/workers/WorkerThread.h b/Source/core/workers/WorkerThread.h
index 83bf3f445e41e95042e7eabd0af2408d8394f039..a58d1e7210f8386f38f266b3ee47b6a08cdb1191 100644
--- a/Source/core/workers/WorkerThread.h
+++ b/Source/core/workers/WorkerThread.h
@@ -35,6 +35,10 @@
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 
+namespace blink {
+class WebWaitableEvent;
+}
+
 namespace WebCore {
 
     class KURL;
@@ -53,6 +57,10 @@ namespace WebCore {
         bool start();
         void stop();
 
+        // Can be used to wait for this worker thread to shut down.
+        // (This is signalled on the main thread, so it's assumed to be waited on the worker context thread)
+        blink::WebWaitableEvent* shutdownEvent() { return m_shutdownEvent.get(); }
+
         bool isCurrentThread() const;
         WorkerRunLoop& runLoop() { return m_runLoop; }
         WorkerLoaderProxy& workerLoaderProxy() const { return m_workerLoaderProxy; }
@@ -93,6 +101,9 @@ namespace WebCore {
         OwnPtr<WorkerThreadStartupData> m_startupData;
 
         NotificationClient* m_notificationClient;
+
+        // Used to signal thread shutdown.
+        OwnPtr<blink::WebWaitableEvent> m_shutdownEvent;
     };
 
 } // namespace WebCore