Use base::size rather than arraysize in third_party/zlib/.

This is purely a mechanical change; there is no intended behavior change.

BUG=837308
R=agl@chromium.org

Change-Id: I1d226c45e473949a8af47311a6e089e5d9df10b4
Reviewed-on: https://chromium-review.googlesource.com/c/1392748
Commit-Queue: Adam Langley <agl@chromium.org>
Reviewed-by: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619414}