It also passes ProfileOAuth2TokenService to another class, FamilyInfoFetcher; that dependency will naturally go away when that class is converted.

Starting to work on this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/300f5a887be2321b53871b008633c07df37695e4

commit 300f5a887be2321b53871b008633c07df37695e4
Author: Julie Jeongeun Kim <jkim@igalia.com>
Date: Mon Jan 07 12:24:37 2019

[s13n] Convert ChildAccountService to IdentityManager

This CL only migrates ChildAccountService production code away from
SigninManager, leaves migration away from ProfileOAuth2TokenService
for a follow up step.

BUG=890795

Change-Id: I1016293bdb1a03cf8be23d51cab2a910af57a2ef
Reviewed-on: https://chromium-review.googlesource.com/c/1393134
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Julie Jeongeun Kim <jkim@igalia.com>
Cr-Commit-Position: refs/heads/master@{#620293}
[modify] https://crrev.com/300f5a887be2321b53871b008633c07df37695e4/chrome/browser/supervised_user/child_accounts/child_account_service.cc

@sdefresne, hi, I'm working on this issue. Could you let me what's supposed to do for 'prefs::kSigninAllowed' on this issue?

I couldn't find 'prefs::kSigninAllowed' in child_account_service.cc, but 'supervised_users::kSigninAllowed'.

If you let me know what to do with it, I could handle it.
Thanks.