Convert supervised_user_service_unittest.cc to Identity service

Replace the calls to SigninManager API to the IdentityManager
one. It's now using a IdentityTestEnvironmentProfileAdaptor to create
the profile used by the tests.

Bug: 903883
Change-Id: Idd2ff37cd4937307369f76783fdada9a9c770946
Reviewed-on: https://chromium-review.googlesource.com/c/1337332
Commit-Queue: Sergio Villar <svillar@igalia.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608713}
1 file changed