Add more functionality to TestURLLoaderFactory

Adding more functionality to TestURLLoaderFactory:
- replacing the existing static SimulateResponse method with
  SimulateResponseForPendingRequest that is easier to use and supports
  setting cookies
- added support for raw headers

This is needed for an upcoming patch that changes GaiaAuthFetcher to
use SimpleURLLoader.

Bug: 840396
TBR=msarda@chromium.org,pmarko@chromium.org

Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: Ice4cc167ebecc7d690e9054a4f2ce0626edbb674
Reviewed-on: https://chromium-review.googlesource.com/1123064
Commit-Queue: Jay Civelli <jcivelli@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Jay Civelli <jcivelli@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574266}
9 files changed