Taking a look...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5

commit c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5
Author: Maks Orlovich <morlovich@chromium.org>
Date: Thu Jul 12 02:45:44 2018

Port GCM's RegistrationRequest to SimpleURLLoader

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

(Other request types will follow; they were not done for now to keep CL size down, since there is a
 lot of wiring of pointers through and test infra stuff).

Bug:  844987 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;luci.chromium.try:linux_mojo;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I1dc5efda6d239509d060f154cedf57ecf73edff2
Reviewed-on: https://chromium-review.googlesource.com/1110705
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Maks Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574468}
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/chrome/browser/extensions/extension_gcm_app_handler_unittest.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/chrome/browser/gcm/gcm_profile_service_unittest.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/chrome/browser/net/system_network_context_manager.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/fake_gcm_client.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/fake_gcm_client.h
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/gcm_client.h
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/gcm_client_impl.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/gcm_client_impl.h
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/gcm_client_impl_unittest.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/gcm_driver_desktop.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/gcm_driver_desktop.h
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/components/gcm_driver/gcm_driver_desktop_unittest.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/google_apis/gcm/BUILD.gn
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/google_apis/gcm/engine/gcm_request_test_base.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/google_apis/gcm/engine/gcm_request_test_base.h
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/google_apis/gcm/engine/registration_request.cc
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/google_apis/gcm/engine/registration_request.h
[modify] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/google_apis/gcm/engine/registration_request_unittest.cc
[add] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/google_apis/gcm/test/DEPS
[add] https://crrev.com/c70c93c4855cbbdd5c9f05fe2f383599be7a0eb5/google_apis/gcm/test/run_all_unittests.cc