[ServiceWorker] Drop client from fetchEvent/request? (#575)

Do we have any good use cases for this?

Talking through with @Hixie & @annevk, communication between request initiator and SW would be better off more granular by setting up a port between the two.

This would be pretty easy with the `fetch` API, but trickier when it comes to elements that trigger requests such as `<img>`.

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/575