CL here: https://chromium-review.googlesource.com/c/chromium/src/+/1288277

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ad01a6979b43aa21cc0f4fc3a41d9441477eef47

commit ad01a6979b43aa21cc0f4fc3a41d9441477eef47
Author: Mario Sanchez Prada <mario@igalia.com>
Date: Fri Oct 19 09:48:11 2018

Convert DiceBrowserTestBase to IdentityManager::Observer

This includes migrating away of SigninManagerBase::Observer as well
as from OAuth2TokenService::Observer, as all APIs in use are now
available via IdentityManager::Observer.

Bug:  887455 
Change-Id: Ia21ae43e5c6a2554e837760485688f917dea1ad8
Reviewed-on: https://chromium-review.googlesource.com/c/1288277
Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#601093}
[modify] https://crrev.com/ad01a6979b43aa21cc0f4fc3a41d9441477eef47/chrome/browser/signin/dice_browsertest.cc