From a conversation with dominickn@:

" I need to ensure that however I convert a GURL to a CSP always matches how it happens to be done here: https://cs.chromium.org/chromium/src/components/content_settings/core/browser/host_content_settings_map.cc?type=cs&l=156 - having crossreferenced and figured out notifications are registered as a 'REQUESTING_ORIGIN_ONLY_SCOPE:'"

"i'm thinking for migration/unmigration, we get all notification settings, then add/remove the channels provider, then set them all on the map"

An easy way to do this would be to have the migration code call HCSM.SetWebsiteSetting instead of inserting prefs into the pref provider directly. More like https://cs.chromium.org/chromium/src/chrome/browser/ssl/chrome_ssl_host_state_delegate.cc?type=cs&l=138 

Is it possible to use the methods in DesktopNotificationProfileUtil - https://cs.chromium.org/chromium/src/chrome/browser/notifications/desktop_notification_profile_util.cc?sq=package:chromium&l=29 ? These are what are used by all the UI-wired code, including on Android when setting/blocking notification settings.