Taking a look...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/278f25742a4c2714d89ff69b486319c448c3bbe9

commit 278f25742a4c2714d89ff69b486319c448c3bbe9
Author: Maks Orlovich <morlovich@chromium.org>
Date: Mon Jul 16 18:18:41 2018

Port GCM's {Checkin, Unregistration}Request to SimpleURLLoader

URLFetcher will stop working with advent of Network Service, and
SimpleURLLoader is the replacement API for most clients.

This also removes the no-longer needed URLRequestContext-based methods
in GCMRequestTestBase, and fixes the regression of CompleteFetch
overrides being bypassed in the previous RegistrationRequest port.

Bug:  844986 ,  844988 

Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: Icdb2e768b274618ce5c6d1fceda6ae9b76c4c275
Reviewed-on: https://chromium-review.googlesource.com/1135291
Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Maks Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575351}
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/components/gcm_driver/gcm_client_impl.cc
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/components/gcm_driver/gcm_client_impl_unittest.cc
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/BUILD.gn
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/checkin_request.cc
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/checkin_request.h
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/checkin_request_unittest.cc
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/gcm_request_test_base.cc
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/gcm_request_test_base.h
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/registration_request_unittest.cc
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/unregistration_request.cc
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/unregistration_request.h
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/engine/unregistration_request_unittest.cc
[add] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/tools/DEPS
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/google_apis/gcm/tools/mcs_probe.cc
[modify] https://crrev.com/278f25742a4c2714d89ff69b486319c448c3bbe9/services/network/test/test_url_loader_factory.cc