This code detects when a user logs in on a site via OAuth. In particular, it detects sites that had successful OAuth login flows using heuristics that observe URL request parameters during navigations. This information is used to trigger Site Isolation for login sites on platforms like Android, where Site Isolation cannot be used for all sites. The login sites are also saved in preferences. Note that the detector's heuristics are not expected to be perfect.
In the future, the OAuth detector should be factored out into its own login detection component under //components, so that it can also be used on platforms such as WebLayer.