Lifetime of service workers in relation to dedicated and shared workers

My apologies. It was in the back of my mind while working on https://github.com/whatwg/html/pull/2520 and yet I forgot to file an issue and coordinate with you all.

It seems you only have one dependency on "the worker's Documents" which is easily replaced in https://w3c.github.io/ServiceWorker/#selection. I guess you might want to say somewhere that a ServiceWorkerGlobalScope object's owner set is always empty. And then you have to define how it's lifetime differs from dedicated and shared workers as currently it builds upon the same infrastructure: https://html.spec.whatwg.org/#the-worker's-lifetime.

That latter part has always been a problem. Perhaps HTML should instead be changed to limit parts of its text around workers to just dedicated and shared workers. It's not entirely clear to me what the right tradeoff is. Hopefully you all can figure that out.

Start with the Service Worker selection section and HTML's “the worker's lifetime” section, along with the linked HTML pull request. Determine how ServiceWorkerGlobalScope owner sets and lifetimes should differ from dedicated and shared workers; done means the relevant specification text and tradeoff are agreed and updated.