Bug 604026 - Sync event loops in workers should be created only if compatible with the worker shutdown status

dom/workers/WorkerRunnable.h

@@ -401,9 +401,12 @@ protected:
 
 public:
   // Dispatch the runnable to the main thread.  If dispatch to main thread
-  // fails, or if the worker is shut down while dispatching, an error will be
-  // reported on aRv.  In that case the error MUST be propagated out to script.
-  void Dispatch(ErrorResult& aRv);
+  // fails, or if the worker is in a state equal or greater of aFailStatus, an
+  // error will be reported on aRv. Normally you want to use 'Terminating' for
+  // aFailStatus, except if you want an infallible runnable. In this case, use
+  // 'Killing'.
+  // In that case the error MUST be propagated out to script.
+  void Dispatch(Status aFailStatus, ErrorResult& aRv);
 
 private:
   NS_IMETHOD Run() override;