owners_finder: Use code-owners plugin if available.

Change-Id: I94d7b3cdc17651a6fe5dafa261c58f46f37b8439
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2693919
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
diff --git a/git_cl.py b/git_cl.py
index 9b943d2..141364b 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -4831,21 +4831,12 @@
     print('\n'.join(owners))
     return 0
 
-  root = settings.GetRoot()
-  owner_files = [f for f in affected_files if 'OWNERS' in os.path.basename(f)]
-  original_owner_files = {
-      f: scm.GIT.GetOldContents(root, f, base_branch).splitlines()
-      for f in owner_files}
-
   return owners_finder.OwnersFinder(
       affected_files,
-      root,
       author,
       [] if options.ignore_current else cl.GetReviewers(),
-      fopen=open,
-      os_path=os.path,
+      cl.owners_client,
       disable_color=options.no_color,
-      override_files=original_owner_files,
       ignore_author=options.ignore_self).run()