They should instead use IdentityManager::Observer API, in detail:

- AccountTrackerService::Observer::OnAccountUpdated()
  => IdentityManager::Observer::OnAccountExtendedInfoUpdated()

- AccountTrackerService::Observer::OnAccountImageUpdated()
  => IdentityManager::Observer::OnAccountExtendedInfoUpdated()

- AccountTrackerService::Observer::OnAccountUpdateFailed()
  => IdentityManager::Observer::OnAccountExtendedInfoUpdated()

- AccountTrackerService::Observer::OnAccountRemoved
  => IdentityManager::Observer::WillRemoveAccountExtendedInfo()