GitLab

URLFetcher will stop working with advent of Network Service, and
SimpleURLLoader is the replacement API for most clients.
This CL migrates PrefetchRequestFetcher et al and the
respective unittests away from URLFetcher.

Bug: 773295,879776
Change-Id: Ibcfc2a7d72b6efe1b372233ade95b58d95fbf62b
Reviewed-on: https://chromium-review.googlesource.com/1215367Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#590048}