GitLab

After this refactoring, SignedExchangeHeader
- Validates response header names and values, and
- Constructs HttpResponseHeaders from the response header map.

Bug: 803774
Change-Id: I25c91db1f07c4fcd0e6c62a9d4aa409838361349
Reviewed-on: https://chromium-review.googlesource.com/958647Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542687}