[Autoroller] Increase flutter roller's AutoRollLastTransition because of license script

Change-Id: I5f2f22fd225171968096946ecbc639b391aa9caa
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/c/179840
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
diff --git a/promk/prometheus/alerts_public.yml b/promk/prometheus/alerts_public.yml
index e916e22..5604346 100644
--- a/promk/prometheus/alerts_public.yml
+++ b/promk/prometheus/alerts_public.yml
@@ -228,15 +228,15 @@
       https://skia.googlesource.com/buildbot/%2B/master/autoroll/PROD.md#error_rate'
 
 # skia-flutter-autoroll takes a long time to transition because it's pre-upload
-# scripts run flutter's license script which can take around 20 minutes.
+# scripts run flutter's license script which can take around 40 minutes.
   - alert: AutoRollLastTransition
-    expr: liveness_last_successful_autoroll_tick_s{roller="skia-flutter-autoroll"} > 30*60
+    expr: liveness_last_successful_autoroll_tick_s{roller="skia-flutter-autoroll"} > 50*60
     labels:
       category: infra
       severity: critical
       owner: rmistry@google.com
     annotations:
-      description: 'Autoroll on {{ $labels.app }} has failed to transition for more than 30 minutes.
+      description: 'Autoroll on {{ $labels.app }} has failed to transition for more than 50 minutes.
       https://console.cloud.google.com/logs/viewer?organizationId=433637338589&project={{ $labels.project }}&minLogLevel=500&resource=container&logName=projects%2Fskia-public%2Flogs%2F{{ $labels.app }}
       '