[owners][git-cl] Use owners client to show all owners for a file.

Change-Id: I04949d95ca466452a58ea91cf2db86852c0621bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2551378
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>
diff --git a/owners_client.py b/owners_client.py
index e5f2be1..49be62f 100644
--- a/owners_client.py
+++ b/owners_client.py
@@ -79,7 +79,7 @@
 
 class DepotToolsClient(OwnersClient):
   """Implement OwnersClient using owners.py Database."""
-  def __init__(self, host, root, fopen, os_path, branch):
+  def __init__(self, host, root, branch, fopen=open, os_path=os.path):
     super(DepotToolsClient, self).__init__(host)
     self._root = root
     self._fopen = fopen