audit: App can load on offline/flaky connection (phase 2)

[paulirish]

Currently we: 1) get all SW registrations 2) filter to to see we have any in an "activated" state. This is good for right now, but it doesn't yet verify that offline caching provided via Service Worker
and it successfully page loads while offline. That'll be the next phase of this test.

Manual evaluation: Flip page offline via DevTools network throttling. Try it out

input:

• all matched SW registrations

audit:

Something like this…

1. flip network throttling to offline.
2. maybe clear disk cache
3. reload the page (or more cleanly: load about:blank and then navigate to the url)
4. network domain can communicate if the page's network request was served via SW.
5. verify its a 200, and page is "good"

when:

• page loaded and in idle state
• everything else is done?

[paulirish]

We can also includes sort of check (from Kinlan's gist):

var allRequestsInCache = () => window.performance.getEntriesByType("resource").every(r => caches.match(new Request(r.name)));

[paulirish]

@paullewis mentioned a simpler detect that seems good:

1. flip network throttling to offline
2. fetch the curent location clientside (fetch itself, yes), and see if it 200s