[ServiceWorker] A header-based SW installation (#685)

It's been discussed as part of the `navigator.connect()` and decided to be proposed as an extension to SW API (v2).

Assuming a communication between a _client_ SW and a _service_ SW is enabled through the efforts in `navigator.connect()`'s persistent channel messaging and the [fallThrough requests proposal](https://github.com/slightlyoff/ServiceWorker/issues/684), the _client_ SWs would need to use readily installed _service_ SWs whenever possible.

Here's a proposal to allow _services_ to install their SWs using HTTP headers when any of their resources are requested: https://github.com/mkruisselbrink/navigator-connect/blob/gh-pages/explainer.md#mommy-where-do-service-workers-come-from

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/685