Currently the Service Worker checks for updates only on SW startup,
an event which happens frequently but also nondeterministically. This
makes it hard for developers to observe the update process or reason
about how updates will be delivered to users. This problem is
exacerbated by the DevTools behavior of keeping the SW alive
indefinitely while opened, effectively preventing the page from
updating at all.
This change causes the SW to additionally check for updates on
navigation requests (app page reloads). This creates deterministic
update behavior, and is much easier for developers to reason about.
It does leave the old update-on-SW-startup behavior in place, as
removing that would be a breaking change.
Fixes#20877
20e1cc049f