Add UMA for how long service workers run for.

content/browser/service_worker/service_worker_metrics.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/service_worker/service_worker_metrics.h"
 
 #include <limits>
 #include <string>
 
 #include "base/metrics/histogram_macros.h"
@@ skipping 960 matching lines @@
           value, max);
     } else {
       UMA_HISTOGRAM_ENUMERATION(
           "ServiceWorker.ContextRequestHandlerStatus.NewWorker."
           "ImportedScript",
           value, max);
     }
   }
 }
 
+void ServiceWorkerMetrics::RecordRuntime(base::TimeDelta time) {
+  // Start at 1 second since we expect service worker to last at least this
+  // long: the update timer and idle timeout timer run on the order of seconds.
+  constexpr base::TimeDelta kMin = base::TimeDelta::FromSeconds(1);
+  // End at 1 day since service workers can conceivably run as long as the the
+  // browser is open; we have to cap somewhere.
+  constexpr base::TimeDelta kMax = base::TimeDelta::FromDays(1);
+  // Set the bucket count to 50 since that is the recommended value for all
+  // histograms.
+  const int kBucketCount = 50;
+
+  UMA_HISTOGRAM_CUSTOM_TIMES("ServiceWorker.Runtime", time, kMin, kMax,
+                             kBucketCount);
+}
+
 }  // namespace content