Add alert for buildbot scheduler

alertserver/alerts.cfg

 # This file defines alerts to be triggered by the server.
 
 #
 # AlertServer should tolerate no errors.
 
 
 [[rule]]
 name = "AlertServer Errors"
 message = "The Error rate for the alertserver is too high, please check the logs."
 database = "graphite"
@@ skipping 754 matching lines @@
 Host info: https://status.skia.org/hosts?filter=%(buildslave)s"""
 database = "skmetrics"
 query = "select mean(value) from \"buildbot.buildsteps.running-time\" where step != 'steps' AND step =~ /wait for device/ AND time > now() - 2m group by builder,master,number,buildslave,step"
 category = "infra"
 condition = "x > 30 * 60 * 1000 * 1000 * 1000"
 actions = ["Email(infra-alerts@skia.org)"]
 auto-dismiss = true
 nag = "1h"
 
 #
+# Buildbot Scheduler
+#
+
+[[rule]]
+name = "Buildbot Scheduler Failing"
+message = "The buildbot scheduler has failed to schedule builds for the last 10 minutes."
+database = "skmetrics"
+query = "select mean(value) from liveness where app='buildbot_scheduler' and host='skia-build-scheduler' and \"name\"='time-since-last-successful-scheduling' and time > now() - 5m group by app, host"
+category = "infra"
+condition = "x > 10 * 60 * 1000 * 1000 * 1000"
+actions = ["Email(infra-alerts@skia.org)"]
+auto-dismiss = true
+nag = "1h"
+
+#
 # CTFE
 #
 
 [[rule]]
 name = "skia-ctfe logserverd"
 message = "skia-ctfe logserverd is not responding at http://skia-ctfe:10115"
 database = "graphite"
 query = "select mean(value) from /^prober$/ where type='failure' AND probename='skia_ctfe_logs' AND time > now() - 10m;"
 category = "infra"
 condition = "x >= 1"
@@ skipping 482 matching lines @@
 [[rule]]
 name = "datahopper_internal Google3-Autoroller up-to-date"
 message = "Commit has not been picked up by Google3-Autoroller for over two hours."
 database = "graphite"
 query = "select mean(value) from /^ingest-build-webhook.oldest-untested-commit-age.value$/ where app='internal' AND host='skia-internal' AND codename='Google3-Autoroller' AND time > now() - 10m"
 category = "infra"
 condition = "x >= 7200"
 actions = ["Email(infra-alerts@skia.org)"]
 auto-dismiss = true
 nag = "1h"