[git-cl][owners] Use new API to suggest batch owners.

Change-Id: I2e2b0aff583e6d9b36261acbef87221e29fe7923
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2565145
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

git_cl.py

@@ -4803,8 +4803,13 @@ def CMDowners(parser, args):
   affected_files = cl.GetAffectedFiles(base_branch)
 
   if options.batch:
-    db = owners.Database(root, open, os.path)
-    print('\n'.join(db.reviewers_for(affected_files, author)))
+    project = cl.GetGerritProject()
+    branch = cl.GetCommonAncestorWithUpstream()
+    client = owners_client.DepotToolsClient(
+        host=cl.GetGerritHost(),
+        root=settings.GetRoot(),
+        branch=branch)
+    print('\n'.join(client.SuggestOwners(project, branch, affected_files)))
     return 0
 
   owner_files = [f for f in affected_files if 'OWNERS' in os.path.basename(f)]

owners_client.py

@@ -148,7 +148,7 @@ class DepotToolsClient(OwnersClient):
 
   def _GetOriginalOwnersFiles(self):
     return {
-      f: scm.GIT.GetOldContents(self._root, f, self._branch)
+      f: scm.GIT.GetOldContents(self._root, f, self._branch).splitlines()
       for _, f in scm.GIT.CaptureStatus(self._root, self._branch)
       if os.path.basename(f) == 'OWNERS'
     }