Remove usage of URLRequestContextGetter in Cast code.

It just needed the NetLog code. Eventually this dependency will go away as well (https://crbug.com/806817).

Bug: 837753
Change-Id: Ic17ada4a10492986f052453ab49111f8732bc7b5
Reviewed-on: https://chromium-review.googlesource.com/c/1363976
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614547}
6 files changed