Notification scheduler: Add metrics for background task.

This CL adds a few metrics to track the behavior of background tasks
for notification scheduling system.

TBR=nikunjb@chromium.org

Bug: 963298
Change-Id: Ic6107269db6eb5fbd70bef2836a18336daef55be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762954Reviewed-by: Hesen Zhang <hesen@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690796}

chrome/browser/notifications/scheduler/internal/notification_scheduler.cc

@@ -21,6 +21,7 @@
 #include "chrome/browser/notifications/scheduler/internal/notification_scheduler_context.h"
 #include "chrome/browser/notifications/scheduler/internal/scheduled_notification_manager.h"
 #include "chrome/browser/notifications/scheduler/internal/scheduler_utils.h"
+#include "chrome/browser/notifications/scheduler/internal/stats.h"
 #include "chrome/browser/notifications/scheduler/public/display_agent.h"
 #include "chrome/browser/notifications/scheduler/public/notification_background_task_scheduler.h"
 #include "chrome/browser/notifications/scheduler/public/notification_params.h"
@@ -171,6 +172,8 @@ class NotificationSchedulerImpl : public NotificationScheduler,
   // NotificationBackgroundTaskScheduler::Handler implementation.
   void OnStartTask(SchedulerTaskTime task_time,
                    TaskFinishedCallback callback) override {
+    stats::LogBackgroundTaskEvent(stats::BackgroundTaskEvent::kStart);
+
     task_start_time_ = task_time;
 
     // Updates the impression data to compute daily notification shown budget.
@@ -182,10 +185,12 @@ class NotificationSchedulerImpl : public NotificationScheduler,
     // Schedule the next background task based on scheduled notifications.
     ScheduleBackgroundTask();
 
+    stats::LogBackgroundTaskEvent(stats::BackgroundTaskEvent::kFinish);
     std::move(callback).Run(false /*need_reschedule*/);
   }
 
   void OnStopTask(SchedulerTaskTime task_time) override {
+    stats::LogBackgroundTaskEvent(stats::BackgroundTaskEvent::kStopByOS);
     task_start_time_ = task_time;
     ScheduleBackgroundTask();
   }
@@ -258,6 +263,7 @@ class NotificationSchedulerImpl : public NotificationScheduler,
     for (const auto& guid : results) {
       context_->notification_manager()->DisplayNotification(guid);
     }
+    stats::LogBackgroundTaskNotificationShown(results.size());
   }
 
   void ScheduleBackgroundTask() {

chrome/browser/notifications/scheduler/internal/stats.cc

@@ -35,6 +35,24 @@ void LogUserAction(const UserActionData& action_data) {
   base::UmaHistogramEnumeration(name, action_data.action_type);
 }
 
+void LogBackgroundTaskEvent(BackgroundTaskEvent event) {
+  UMA_HISTOGRAM_ENUMERATION("Notifications.Scheduler.BackgroundTask.Event",
+                            event);
+
+  if (event == BackgroundTaskEvent::kStart) {
+    base::Time::Exploded explode;
+    base::Time::Now().LocalExplode(&explode);
+    UMA_HISTOGRAM_EXACT_LINEAR("Notifications.Scheduler.BackgroundTask.Start",
+                               explode.hour, 24);
+  }
+}
+
+void LogBackgroundTaskNotificationShown(int shown_count) {
+  UMA_HISTOGRAM_CUSTOM_COUNTS(
+      "Notifications.Scheduler.BackgroundTask.NotificationShown", shown_count,
+      0, 10, 11);
+}
+
 void LogImpressionDbInit(bool success, int entry_count) {
   UMA_HISTOGRAM_BOOLEAN("Notifications.Scheduler.ImpressionDb.InitResult",
                         success);

chrome/browser/notifications/scheduler/internal/stats.h

@@ -10,6 +10,19 @@
 namespace notifications {
 namespace stats {
 
+// Events to track behavior of the background task used by notification
+// scheduling system. Used in histograms, don't reuse or delete values. Needs to
+// match NotificationSchedulerBackgroundTaskEvent in enums.xml.
+enum class BackgroundTaskEvent {
+  // Background task starts.
+  kStart = 0,
+  // Background task finishes and stopped gracefully.
+  kFinish = 1,
+  // The background task is stopped by the OS without finishing the its job.
+  kStopByOS = 2,
+  kMaxValue = kStopByOS
+};
+
 // Used to log events in impression tracker. Don't reuse or delete values. Needs
 // to match NotificationSchedulerImpressionEvent in enums.xml.
 enum class ImpressionEvent {
@@ -26,6 +39,13 @@ enum class ImpressionEvent {
 // scheduling system.
 void LogUserAction(const UserActionData& user_action_data);
 
+// Logs events to track the behavior of the background task used by notification
+// scheduling system.
+void LogBackgroundTaskEvent(BackgroundTaskEvent event);
+
+// Logs the number of notification shown in the current background task.
+void LogBackgroundTaskNotificationShown(int shown_count);
+
 // Logs the initialization result for impression database.
 void LogImpressionDbInit(bool success, int entry_count);
 

tools/metrics/histograms/enums.xml

@@ -43438,6 +43438,12 @@ Called by update_net_trust_anchors.py.-->
   <int value="5" label="Chrome process launch failed"/>
 </enum>
 
+<enum name="NotificationSchedulerBackgroundTaskEvent">
+  <int value="0" label="Start"/>
+  <int value="1" label="Finish"/>
+  <int value="2" label="Stop by OS"/>
+</enum>
+
 <enum name="NotificationSchedulerImpressionEvent">
   <int value="0" label="New suppression"/>
   <int value="1" label="Suppression released"/>

tools/metrics/histograms/histograms.xml

@@ -86856,6 +86856,35 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="Notifications.Scheduler.BackgroundTask.Event"
+    enum="NotificationSchedulerBackgroundTaskEvent" expires_after="2020-08-01">
+  <owner>xingliu@chromium.org</owner>
+  <owner>hesen@chromium.org</owner>
+  <summary>
+    Records the various events when running the background task in notification
+    scheduling system.
+  </summary>
+</histogram>
+
+<histogram name="Notifications.Scheduler.BackgroundTask.NotificationShown"
+    units="notifications" expires_after="2020-08-01">
+  <owner>xingliu@chromium.org</owner>
+  <owner>hesen@chromium.org</owner>
+  <summary>
+    Records the number of notifications shown in each background task run.
+  </summary>
+</histogram>
+
+<histogram name="Notifications.Scheduler.BackgroundTask.Start" units="hours"
+    expires_after="2020-08-01">
+  <owner>xingliu@chromium.org</owner>
+  <owner>hesen@chromium.org</owner>
+  <summary>
+    Records the hour (0-23) when the notification scheduler background task
+    starts.
+  </summary>
+</histogram>
+
 <histogram name="Notifications.Scheduler.Impression.Count" units="records"
     expires_after="2020-08-01">
 <!-- Name completed by histogram_suffixes name="NotificationSchedulerClientType" -->