This can go into IdentityManager::DiagnosticsObserver.

Working on this

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2da1b80de574746633024349f86976b9deba16dd

commit 2da1b80de574746633024349f86976b9deba16dd
Author: Sergio Villar Senin <svillar@igalia.com>
Date: Mon Dec 10 10:05:08 2018

Replace SigninManager::DiagnosticsObserver::NotifySigninValueChanged API

Clients should use the new equivalent API in
IdentityManager::DiagnosticsObserver.

Bug:  907004 
Change-Id: Ic9b69820fdc8974bdade256eadd08eeb64acbb72
Reviewed-on: https://chromium-review.googlesource.com/c/1361066
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#615074}
[modify] https://crrev.com/2da1b80de574746633024349f86976b9deba16dd/chrome/browser/signin/about_signin_internals_factory.cc
[modify] https://crrev.com/2da1b80de574746633024349f86976b9deba16dd/chrome/browser/signin/dice_response_handler_unittest.cc
[modify] https://crrev.com/2da1b80de574746633024349f86976b9deba16dd/components/signin/core/browser/about_signin_internals.cc
[modify] https://crrev.com/2da1b80de574746633024349f86976b9deba16dd/components/signin/core/browser/about_signin_internals.h
[modify] https://crrev.com/2da1b80de574746633024349f86976b9deba16dd/ios/chrome/browser/signin/about_signin_internals_factory.cc
[modify] https://crrev.com/2da1b80de574746633024349f86976b9deba16dd/services/identity/public/cpp/DEPS
[modify] https://crrev.com/2da1b80de574746633024349f86976b9deba16dd/services/identity/public/cpp/identity_manager.cc
[modify] https://crrev.com/2da1b80de574746633024349f86976b9deba16dd/services/identity/public/cpp/identity_manager.h