Add OWNERS to ARC storage directories

BUG=b:116761000
TEST=None

Change-Id: Id16dd20f0cf242ebed23a1521c7bbf60ba16f308
Reviewed-on: https://chromium-review.googlesource.com/1250967Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Shuhei Takahashi <nya@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595388}

chrome/browser/chromeos/arc/downloads_watcher/OWNERS

+hashimoto@chromium.org
+nya@chromium.org

chrome/browser/chromeos/arc/fileapi/OWNERS

+hashimoto@chromium.org
+nya@chromium.org

components/arc/disk_quota/OWNERS

+hashimoto@chromium.org

components/arc/obb_mounter/OWNERS

+hashimoto@chromium.org

components/arc/storage_manager/OWNERS

+hashimoto@chromium.org

components/arc/volume_mounter/OWNERS

+hashimoto@chromium.org
+
 per-file *_struct_traits*.*=set noparent
 per-file *_struct_traits*.*=file://ipc/SECURITY_OWNERS
 per-file *_struct_traits*.*=file://components/arc/common/ARC_SECURITY_OWNERS