Update service worker to perform caching activities in install event

[jonahwilliams]

The service worker event activate is not guaranteed to run to completion, for example if the browser closes. If it fails or ends early, then it will never be rerun.

The install event has stronger guarantees, and is a better solution for updating the caches.

[jonahwilliams]

activate could be updated to only perform cleanup

[jeffposnick]

Congrats on the Flutter 2 PWA launch!

I was taking a look at the service worker for one of the sample apps, which I assume is representative of all Flutter PWAs.

Unfortunately, the activate handler is still being used for critical cache manipulation, not just cleanup. I've mentioned this elsewhere, but putting any data operations that require guaranteed completion inside of activate handler risks cache inconsistency, as we experienced in the Workbox project (GoogleChrome/workbox#1793).

Apologies if I'm misreading your service worker, but based on the fact that this issue is still open, I'm assuming that I'm correct in that assessment.