Taking this

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d3fc2ab8a4a911bdf26c1763e476205d732f30bd

commit d3fc2ab8a4a911bdf26c1763e476205d732f30bd
Author: Sergio Villar Senin <svillar@igalia.com>
Date: Tue Oct 16 18:41:02 2018

Convert assistant_optin_utils.cc to IdentityManager

It was using SigninManagerBase API to get the primary (authenticated)
account id. It's now using the IdentityManager API.

Bug:  890806 
Change-Id: I2902cd16c4040301f84d238dc46ca2b8f9e10793
Reviewed-on: https://chromium-review.googlesource.com/c/1276609
Commit-Queue: Sergio Villar <svillar@igalia.com>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600058}
[modify] https://crrev.com/d3fc2ab8a4a911bdf26c1763e476205d732f30bd/chrome/browser/ui/webui/chromeos/assistant_optin/assistant_optin_utils.cc

Closing