Add zlib_bench OWNERS

Per crbug.com/798943#c9 zlib_bench contains the snappy bench verbatim,
for the reasons explained there. However, subsequent code changes were
not cc-ed to me. Add an OWNERS file to vet changes.

Bug: 798943
Change-Id: I51b68f78190b1277882e5aeeffdc7b4e377c630d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1746510
Commit-Queue: Chris Blume <cblume@chromium.org>
Auto-Submit: Noel Gordon <noel@chromium.org>
Reviewed-by: Chris Blume <cblume@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686266}

third_party/zlib/contrib/bench/OWNERS

+noel@chromium.org