Add chrome/browser/chromeos/arc/wallpaper/OWNERS

BUG=b:116761000
TEST=None

Change-Id: Ic4c2fbc0a2fe17cb02e09539ef4c65ae1f4d50de
Reviewed-on: https://chromium-review.googlesource.com/1251225Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Daichi Hirono <hirono@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595378}

chrome/browser/chromeos/arc/wallpaper/OWNERS

+hidehiko@chromium.org
+hirono@chromium.org