Service worker doesn't precache content

How do we add separate content pages to the service worker cache? Currently it works great for accessed pages/media, but not for pages that haven't been accessed.

Start at the service worker entry point and trace how accessed pages and media are added to the cache. Reproduce the behavior with a content page that has not been visited, then verify that separate content pages are available offline after precaching.

Written by the indexing model from the issue text.