Migrate AutofillDownloadManager to SimpleURLLoader

This CL migrates AutofillDownloadManager away from URLFetcher, to
SimpleURLLoader.

As a notorious remark, the CL introduces a public method to
SimpleURLLoader, LoadedFromCache. It allows to verify whether
some specific content are served from the cache, as expected.

BUG=773295,844929

Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: I92a36bc032b7c0e182ae83f367eefd605ad888ca
Reviewed-on: https://chromium-review.googlesource.com/1114998
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#575269}
9 files changed