Allow items passed to precache to be Promises, either for URLs or arrays of URLs

[wibblymat]

Perhaps you need to do some async operation, such as reading IDB, before you can get your list of resources to cache. In that case you should be able to pass a Promise for the list to precache, and the install event will wait for them to resolve during the event.waitUntil period.

[wibblymat]

Dealt with in new repo