This will require changing the class to receive an IdentityManager instead of SigninManager, ProfileOAuth2TokenService and AccountTrackerService.

Methods with replacements:
- SigninManager::GetAuthenticatedAccountId
  => IdentityManager::GetPrimaryAccountId
- SigninManager::OnExternalSigninCompleted
  => PrimaryAccountMutator::SetPrimaryAccount
- SigninManager::SignOut
  => PrimaryAccountMutator::ClearPrimaryAccount
- AccountTrackerService::GetAccountInfo
  => IdentityManager::GetAccountInfoForAccountWithRefreshToken

Methods with no replacements:
- AccountTrackerService::SeedAccountInfo
- ProfileOAuth2TokenServiceIOSDelegate::ReloadCredentials