Add ServiceWorker Static Routing API support

[sisidovski]

We propose ServiceWorker static routing API, which allows developers to configure routing, and offload things ServiceWorkers do. The main spec update is in w3c/ServiceWorker#1701, but some behavior involves the fetch spec change (specifically, "race-network-and-fetch-handler" option).

• At least two implementers are interested (and none opposed):
  • Chrome is proposing this change https://groups.google.com/a/chromium.org/g/blink-dev/c/-SEMMttEqz4
  • Mozilla Service Worker Static Routing API (positive) mozilla/standards-positions#894
• Tests are written and can be reviewed and commented upon at:
  • https://github.com/web-platform-tests/wpt/tree/master/service-workers/service-worker/tentative/static-router
• Implementation bugs are filed:
  • Chromium: crbug.com/40241479
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1855580
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=269893
  • Deno (not for CORS changes): N/A, Deno doesn't implement ServiceWorker.
• MDN issue is filed: Add docs for service worker static routing API mdn/mdn#527
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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[domenic]

Non-editor LGTM

[annevk]

Wouldn't this return a response without any filtering getting applied? I guess the idea is that these are already filtered responses? Can that be asserted?

[annevk]

As far as I can tell https://w3c.github.io/ServiceWorker/#lookup-race-response-algorithm ends up waiting, which would delay this algorithm. Is that really the intent?