Allow TestURLLoaderFactory::SimulateResponse's mock responses to fail

This CL makes the TestURLLoaderFactory::SimulateResponse API more flexible in the following ways:

- it starts to actually use the |net_error| parameter (to build the URLLoaderCompletionatus
  instance)
- it adds an extra (also optional) net::HttpStatusCode parameter, so that
  one can more easily mock failing responses.
- one can see it in action in [1].

[1] https://crrev.com/c/1114998/components/autofill/core/browser/autofill_download_manager_unittest.cc#283

Bug: 773295
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: Iba4edf640b3ff82e035ffbe26c3066d404f18ce7
Reviewed-on: https://chromium-review.googlesource.com/1120916
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571635}
2 files changed