Filter out no-cors requests from the race-network-request

[sisidovski]

This will address the comment in whatwg/fetch#1737 (comment).

When "race-network-request" is matched as the router rule, the service worker starts a network request in parallel with dispatching the fetch event. The response is keyed by request and managed in race response map. And the fetch API will check this map whether the request is already started by the service worker, and use its response if the corresponding entry is found.

We use ok-status to tell if the response is successful or not, and use the response only when the status is ok-status. This is needed to support the offline capability. However, with the request mode "no-cors", the response will be filtered. The filtered response's status is always 0, so this is handled as a failure in "race-network-request" even without this change. But it would be better that we explicitly filter out "no-cors" in the handle fetch algorithm.

Once we get an agreement to this change, I'll add a WPT and fix Chrome behavior.

---

Preview | Diff

[yoshisatoyanagisawa]

You intend to make all "no-cors" (i.e. cross origin resource fetches) requests to fallback to fetch handler even if the race-network-and-fetch-handler source is set, right?