Currently we have no plan for sites that were Added to Desktop as shortcuts to upgrade into PWAs (which can happen for old Bookmark Apps, or for new Bookmark Apps which then get manifests + serviceworkers).

Some options are:
- Automatically upgrade (this would be jarring as link capturing and launch type would suddenly change)
- Ensure sites are able to prompt to install (currently, they don't because they are considered installed, even if they're not PWAs and install surfaces don't appear)
- Add a page action, possibly with a message or bubble, in both the omnibox and the hosted app frame that an upgrade is available.
- Do nothing. Users need to uninstall and reinstall to get the new experience.