Network Error Logging: Fill in protocol field

If ALPN protocol negotiation gives us an answer, use that directly;
otherwise, we assume HTTP/1.1 if any response headers were received.

Bug: 748549,833996
Change-Id: I33d6217ede6202358acf1a343296f5019a9b6052
Reviewed-on: https://chromium-review.googlesource.com/998021
Commit-Queue: Douglas Creager <dcreager@google.com>
Reviewed-by: Julia Tuttle <juliatuttle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551505}
4 files changed