Set OWNERS to file manager OWNERS

Bug: None
Change-Id: Ia4bf1985967999b9542a6ba172eccd6f3007aabb
Reviewed-on: https://chromium-review.googlesource.com/1237900Reviewed-by: Naoki Fukino <fukino@chromium.org>
Commit-Queue: Sergei Datsenko <dats@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593091}

chrome/browser/chromeos/fileapi/OWNERS

-fukino@chromium.org
-yamaguchi@chromium.org
-
+file://ui/file_manager/OWNERS