Set ios/chrome/test/BUILD.gn OWNERS to *.

It is common practice to allow everyone to review BUILD.gn files.

Change-Id: I8639deb0ed5920948a9703e34fbf5991f105244e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1643841Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666149}

ios/chrome/test/OWNERS

 eugenebut@chromium.org
 
+# This is for the common case of adding or renaming files. If you're doing
+# structural changes, use usual OWNERS rules.
+per-file BUILD.gn=*
+
 # TEAM: ios-directory-owners@chromium.org
 # OS: iOS