The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d5b3f0b359aacd85faf346458dd52e6740cda1e4

commit d5b3f0b359aacd85faf346458dd52e6740cda1e4
Author: Jay Civelli <jcivelli@google.com>
Date: Thu Mar 01 19:05:55 2018

Add a response started callback to SimpleURLLoader

Adding a callback to SimpleURLLoader to get notified when the request
started, i.e. when the headers are available.

Bug:  817458 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I1b53ba5b64a4c1cc406d03638f733a177ec863be
Reviewed-on: https://chromium-review.googlesource.com/941881
Commit-Queue: Jay Civelli <jcivelli@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540239}
[modify] https://crrev.com/d5b3f0b359aacd85faf346458dd52e6740cda1e4/services/network/public/cpp/simple_url_loader.cc
[modify] https://crrev.com/d5b3f0b359aacd85faf346458dd52e6740cda1e4/services/network/public/cpp/simple_url_loader.h
[modify] https://crrev.com/d5b3f0b359aacd85faf346458dd52e6740cda1e4/services/network/public/cpp/simple_url_loader_unittest.cc