autotest: add a monarch stat for scheduler tick

BUG=None
TEST=None

Change-Id: I6c80490c6dd9dbc9cb8ec461266a913ca8d44b61
Reviewed-on: https://chromium-review.googlesource.com/357110
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@google.com>
diff --git a/scheduler/monitor_db.py b/scheduler/monitor_db.py
index d520a40..413c0d8 100755
--- a/scheduler/monitor_db.py
+++ b/scheduler/monitor_db.py
@@ -19,6 +19,7 @@
 from autotest_lib.frontend import setup_django_environment
 
 import django.db
+from chromite.lib import metrics
 from chromite.lib import ts_mon_config
 
 from autotest_lib.client.common_lib import control_data
@@ -386,6 +387,7 @@
         with timer.get_client('django_db_reset_queries'):
             django.db.reset_queries()
         self._tick_count += 1
+        metrics.Counter('chromeos/autotest/scheduler/tick').increment()
 
 
     def _run_cleanup(self):