Add Net.SpdyResponseCode histogram to track HTTP/2 response codes.

This would be useful to see how often servers send a 103 Early Hints
response (to be able to better prioritize implementing support), and to
see how often servers send a 101 Switching Protocols response (which
means their WebSocket over HTTP/2 implementation is broken), and a whole
bunch of other things.

Bug: 671310, 801564
Change-Id: I9e66acb6405793c4b3c12cf9d5b32edb2262c70b
Reviewed-on: https://chromium-review.googlesource.com/1087583
Reviewed-by: Zhongyi Shi <zhongyi@chromium.org>
Reviewed-by: Gayane Petrosyan <gayane@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565179}
3 files changed