SigninPromo gets account info from AccountTrackerService for a given AccountID. Its signin_manager.h inclusions looks stale. To do this conversion, we need to have our solution for synchronous access to account info from account ID in place.

signin_promo_util.cc checks whether the user is authenticated, whether auth is ongoing, and whether signin is allowed in order to determine whether to show the signin promo. To do this conversion, we need our solutions for access to whether auth is ongoing and whether signin is allowed in place.