CL here: https://chromium-review.googlesource.com/c/chromium/src/+/1286824

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2f09488387f03cb6152f730566752f5f7cdcadaf

commit 2f09488387f03cb6152f730566752f5f7cdcadaf
Author: Mario Sanchez Prada <mario@igalia.com>
Date: Mon Nov 05 17:05:44 2018

Convert SyncEngine to IdentityManager::Observer

Converted implementations for GoogleSigninFailed, GoogleSigninSucceeded
and GoogleSignedOut, and updated unit tests accordingly.

Bug:  887457 
Change-Id: I9ced1e6e5b91d5b05dd10b4520201b48e202fe75
Reviewed-on: https://chromium-review.googlesource.com/c/1286824
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Taiju Tsuiki <tzik@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#605365}
[modify] https://crrev.com/2f09488387f03cb6152f730566752f5f7cdcadaf/chrome/browser/apps/platform_apps/api/sync_file_system/sync_file_system_browsertest.cc
[modify] https://crrev.com/2f09488387f03cb6152f730566752f5f7cdcadaf/chrome/browser/sync_file_system/drive_backend/sync_engine.cc
[modify] https://crrev.com/2f09488387f03cb6152f730566752f5f7cdcadaf/chrome/browser/sync_file_system/drive_backend/sync_engine.h