[variations] Use base::size() instead of arraysize

arraysize is deprecated, we should use base::size() instead.
This cl clears a presubmit warnings.

Bug: 837308
Change-Id: I5479c0f16e6df0b43b617c0e15c6c28527c41cbd
Reviewed-on: https://chromium-review.googlesource.com/1213622
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Byoungkwon Ko <codeimpl@gmail.com>
Cr-Commit-Position: refs/heads/master@{#590160}
9 files changed