Log UMA for notification trigger display delay.

This adds UMA to track the actual display delay of notifications with
show triggers.

Bug: 891339
Change-Id: I8263b9b50df06eabb38079641069863d74d26327
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1801758Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Richard Knoll <knollr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699084}

content/browser/notifications/platform_notification_context_impl.cc

@@ -438,6 +438,11 @@ void PlatformNotificationContextImpl::DoTriggerNotification(
     return;
   }
 
+  base::Time timestamp =
+      database_data.notification_data.show_trigger_timestamp.value();
+  UMA_HISTOGRAM_LONG_TIMES("Notifications.Triggers.DisplayDelay",
+                           base::Time::Now() - timestamp);
+
   // Remove resources from DB as we don't need them anymore.
   database_->DeleteNotificationResources(write_database_data.notification_id,
                                          write_database_data.origin);

content/browser/notifications/platform_notification_context_trigger_unittest.cc

@@ -7,6 +7,7 @@
 #include "base/bind.h"
 #include "base/run_loop.h"
 #include "base/test/bind_test_util.h"
+#include "base/test/metrics/histogram_tester.h"
 #include "base/test/scoped_feature_list.h"
 #include "base/time/time.h"
 #include "content/browser/notifications/notification_trigger_constants.h"
@@ -277,4 +278,22 @@ TEST_F(PlatformNotificationContextTriggerTest, EnforcesLimitOnUpdate) {
           TimeDelta::FromSeconds(kMaximumScheduledNotificationsPerOrigin + 1)));
 }
 
+TEST_F(PlatformNotificationContextTriggerTest, RecordDisplayDelay) {
+  base::HistogramTester histogram_tester;
+  base::TimeDelta trigger_delay = TimeDelta::FromSeconds(10);
+  base::TimeDelta display_delay = TimeDelta::FromSeconds(8);
+
+  WriteNotificationData("1", Time::Now() + trigger_delay);
+  ASSERT_EQ(0u, GetDisplayedNotifications().size());
+
+  // Forward time until after the expected trigger time.
+  task_environment_.FastForwardBy(trigger_delay + display_delay);
+
+  // Trigger notification |display_delay| after it should have been displayed.
+  TriggerNotifications();
+
+  histogram_tester.ExpectUniqueSample("Notifications.Triggers.DisplayDelay",
+                                      display_delay.InMilliseconds(), 1);
+}
+
 }  // namespace content

tools/metrics/histograms/histograms.xml

@@ -89628,6 +89628,16 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="Notifications.Triggers.DisplayDelay" units="ms"
+    expires_after="M82">
+  <owner>knollr@chromium.org</owner>
+  <owner>peter@chromium.org</owner>
+  <summary>
+    Delay between the expected and actual display time of a notification.
+    Recorded just before displaying a notification with a show trigger.
+  </summary>
+</histogram>
+
 <histogram name="Notifications.Triggers.HasShowTrigger" enum="Boolean"
     expires_after="M80">
   <owner>knollr@chromium.org</owner>