By the way, anyone can start on the changes to the production code right away, but avoid trying to change signin_tracker_unittest.cc until I've fixed  crbug.com/893141  (which should happen very quickly).

Camille, this is a nice conversion starter bug. The migration doc for doing the conversions is here: https://docs.google.com/document/d/14f3qqkDM9IE4Ff_l6wuXvCMeHfSC9TxKezXTCyeaPUY/edit#.

It has info on porting the observers as well as porting the unittest to use IdentityTestEnvironment.

 Issue 797954  has been merged into this issue.

Camille has started this in https://chromium-review.googlesource.com/c/chromium/src/+/1291313.

I just realized that since SigninTracker is inside //components/signin/core/browser, landing the conversion is blocked on  https://crbug.com/901859 . I'm actively working on that split and hope to unblock this by EOW. In the meantime, we can still push forward on the CL, especially because the precursor parts (either removing the dependency on GaiaCookieManagerService or bringing up the needed APIS in IdentityManager) are not blocked on  https://crbug.com/901859  in any way.

The complete conversion is blocked on developing an API to replace usage of GaiaCookieManagerService::Observer. Camille: in the meantime you can push forward the CL that you have; if you rebase you'll bring in my fixes for  crbug.com/901859 .

Spoke with Camille offline and we're going to free this up for a vendor to take. Please feel free (and I recommend!) to use Camille's in-progress CL as a building block: https://chromium-review.googlesource.com/c/chromium/src/+/1291313.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/02b7b229108e172bad94a560ed6393e107afc7af

commit 02b7b229108e172bad94a560ed6393e107afc7af
Author: Antonio Gomes <tonikitoo@igalia.com>
Date: Thu Jan 10 12:12:07 2019

[s13n] Convert SigninTracker to observing IdentityManager

IdentityManager is implemented on top of SigninManager, PO2TS,
GaiaCookieServiceManager, etc, in the servicified world.

This CL convers SigninTracker away from the aforementioned classes
to use the IdentityManager API.

BUG= 893133 

Change-Id: Ia1f02a35a3a740b479cabba89ade0ff0ff0e85a5
Reviewed-on: https://chromium-review.googlesource.com/c/1403159
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#621551}
[modify] https://crrev.com/02b7b229108e172bad94a560ed6393e107afc7af/chrome/browser/signin/signin_tracker_factory.cc
[modify] https://crrev.com/02b7b229108e172bad94a560ed6393e107afc7af/components/signin/core/browser/signin_tracker.cc
[modify] https://crrev.com/02b7b229108e172bad94a560ed6393e107afc7af/components/signin/core/browser/signin_tracker.h
[modify] https://crrev.com/02b7b229108e172bad94a560ed6393e107afc7af/components/signin/core/browser/signin_tracker_unittest.cc