I'd like to take over this bug.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eabdd180c1699d037dc4f94932047289a16aad16

commit eabdd180c1699d037dc4f94932047289a16aad16
Author: Gyuyoung Kim <gyuyoung@igalia.com>
Date: Wed Jan 16 02:40:23 2019

s13n: Remove unnecessary signin_manager related includes in signin_promo.cc

This CL cleans up the unnecessary includes related to SigninManager.

Bug:  920226 
Change-Id: Id64f444591456e42da80abf26f0f03c6ef45fe4b
Reviewed-on: https://chromium-review.googlesource.com/c/1410712
Commit-Queue: Gyuyoung Kim <gyuyoung@igalia.com>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623061}
[modify] https://crrev.com/eabdd180c1699d037dc4f94932047289a16aad16/chrome/browser/signin/signin_promo.cc