[ServiceWorker] What happens if a method is called & the parent window is gone (#722)

* Get method from same origin iframe
* Iframe client closes/navigates
* What happens when this method is called?

It should fail. This is a bigger problem than just SW, many DOM APIs have this problem (eg new Worker).

We *may* get this for free from IDL, but we're not sure.

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/722