Network Service: Document how adding/removing http headers for web content requests are implemented

This is a follow-up CL per comments at:
https://chromium-review.googlesource.com/c/chromium/src/+/1120955

This CL adds comments to //components/variations/variations_http_header_provider.cc
to document how adding/removing http headers for web content requests are
implemented differently when Network Service is enabled or not enabled.

Bug: 841309
Change-Id: I6b1e7ac776415131f6f549253f8a69a4d0992117
Reviewed-on: https://chromium-review.googlesource.com/1134408
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Jun Cai <juncai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574602}
1 file changed