GitLab

Also change identity::ClearPrimaryAccount to work on a SigninManager,
so I can use it in tests that have a production SigninManager.

BUG=801971
R=blundell@chromium.org

Change-Id: I49176bd7e50a0e7c208403e276371bf93822fde6
Reviewed-on: https://chromium-review.googlesource.com/1143268
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577521}