Remove a bunch of StoragePartition::GetURLRequestContext calls when the network service is enabled.

This will eventually be 0 and then we can DCHECK, but is currently blocked on a few things (see blocking bugs).

Bug: 837753
Change-Id: I078cba0cf622cd9f2baf084f6c1d371b5e44457a
Reviewed-on: https://chromium-review.googlesource.com/c/1351774
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611299}
19 files changed