Explicit notification and removal of lifecycle observers.

Source/core/workers/WorkerGlobalScope.h

Index: Source/core/workers/WorkerGlobalScope.h
diff --git a/Source/core/workers/WorkerGlobalScope.h b/Source/core/workers/WorkerGlobalScope.h
index 915e779503eb82e08e4043ba6b9a431b726d1ea1..9a39bc395a777695e4a5e182f9104cdd900b8238 100644
--- a/Source/core/workers/WorkerGlobalScope.h
+++ b/Source/core/workers/WorkerGlobalScope.h
@@ -150,6 +150,8 @@ namespace WebCore {
         virtual EventTarget* errorEventTarget() OVERRIDE FINAL;
         virtual void didUpdateSecurityOrigin() OVERRIDE FINAL { }
 
+        void clearThread() { m_thread = 0; }
+
         KURL m_url;
         String m_userAgent;