spec behavior when ServiceWorkerContainer parent client is dead #777

This is kind of a corner case, but I don't think the spec really handles it currently:

1. open a random webpage
2. w = window.open("./")
3. sw = w.navigator.serviceWorker
4. close the new tab from step 1
5. sw.register("whatever.js");

In this case we're calling .register() for a window that is already closed. I'm intending to reject with InvalidStateErr, but I guess it would be nice to spec it.