SigninManager::OnExternalSigninCompleted(..)

should be replaced by 

  auto* primary_account_mutator = IdentityManager::GetPrimaryAccountMutator();
  primary_account_mutator->SetPrimaryAccount(account_info_.account_id);

+1

Hi Colin,
I couldn't find secondary_account_sync_test.cc file. Are you referring secondary_account_helper.cc here ?

Hi,

Yes, the CL introducing this class got reverted. You can make the change in secondary_account_helper.cc. Thanks!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e2d74c0819cff1aed390a8f980f6dedcaa2ffb01

commit e2d74c0819cff1aed390a8f980f6dedcaa2ffb01
Author: Abhijeet Kandalkar <abhijeet@igalia.com>
Date: Mon Jan 21 12:26:17 2019

Port secondary_account_helper.cc away from using SigninManager

This CL switches the secondary_account_helper from using
SigninManagerFactory in favor of the new IdentityManager.

Bug:  920275 
Change-Id: Id35cecb024ad584d06fcf6f4a1ee359799fef40b
Reviewed-on: https://chromium-review.googlesource.com/c/1408692
Commit-Queue: Abhijeet Kandalkar <abhijeet@igalia.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624565}
[modify] https://crrev.com/e2d74c0819cff1aed390a8f980f6dedcaa2ffb01/chrome/browser/sync/test/integration/secondary_account_helper.cc