If the local state can't be read in, and reverts to default values, the default_opt_in pref value is lost.

On windows, the value could be restored from the AP value that originally provided the default_opt_in value.

Other platforms would need to back it up in another place to be able to recover. The only other platform where we are probably concerned about this would be android, and it doesn't seem like it would be problematic there (but it does occur according to PrefService.ReadError).