[Background Sync] Record number of batched sync events in UMA

BUG=490482

Review URL: https://codereview.chromium.org/1251523002

Cr-Commit-Position: refs/heads/master@{#339880}

4 files changed, 46 insertions, 31 deletions

diff --git a/content/browser/background_sync/background_sync_manager.cc b/content/browser/background_sync/background_sync_manager.cc
index 7903aa4..960c63f8 100644
--- a/content/browser/background_sync/background_sync_manager.cc
+++ b/content/browser/background_sync/background_sync_manager.cc
@@ -799,29 +799,37 @@ void BackgroundSyncManager::FireReadyEventsImpl(const base::Closure& callback) {
     }
   }
 
-  base::TimeTicks start_time = base::TimeTicks::Now();
-
-  // Fire the sync event of the ready registrations and run |callback| once
-  // they're all done.
-  base::Closure events_fired_barrier_closure =
-      base::BarrierClosure(sw_id_and_keys_to_fire.size(), base::Bind(callback));
-
-  // Record the total time taken after all events have run to completion.
-  base::Closure events_completed_barrier_closure =
-      base::BarrierClosure(sw_id_and_keys_to_fire.size(),
-                           base::Bind(&OnAllSyncEventsCompleted, start_time));
-
-  for (const auto& sw_id_and_key : sw_id_and_keys_to_fire) {
-    int64 service_worker_id = sw_id_and_key.first;
-    const BackgroundSyncRegistration* registration =
-        LookupRegistration(service_worker_id, sw_id_and_key.second);
-
-    service_worker_context_->FindRegistrationForId(
-        service_worker_id, sw_to_registrations_map_[service_worker_id].origin,
-        base::Bind(&BackgroundSyncManager::FireReadyEventsDidFindRegistration,
-                   weak_ptr_factory_.GetWeakPtr(), sw_id_and_key.second,
-                   registration->id(), events_fired_barrier_closure,
-                   events_completed_barrier_closure));
+  // If there are no registrations currently ready, then just run |callback|.
+  // Otherwise, fire them all, and record the result when done.
+  if (sw_id_and_keys_to_fire.size() == 0) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
+                                                  base::Bind(callback));
+  } else {
+    base::TimeTicks start_time = base::TimeTicks::Now();
+
+    // Fire the sync event of the ready registrations and run |callback| once
+    // they're all done.
+    base::Closure events_fired_barrier_closure = base::BarrierClosure(
+        sw_id_and_keys_to_fire.size(), base::Bind(callback));
+
+    // Record the total time taken after all events have run to completion.
+    base::Closure events_completed_barrier_closure =
+        base::BarrierClosure(sw_id_and_keys_to_fire.size(),
+                             base::Bind(&OnAllSyncEventsCompleted, start_time,
+                                        sw_id_and_keys_to_fire.size()));
+
+    for (const auto& sw_id_and_key : sw_id_and_keys_to_fire) {
+      int64 service_worker_id = sw_id_and_key.first;
+      const BackgroundSyncRegistration* registration =
+          LookupRegistration(service_worker_id, sw_id_and_key.second);
+
+      service_worker_context_->FindRegistrationForId(
+          service_worker_id, sw_to_registrations_map_[service_worker_id].origin,
+          base::Bind(&BackgroundSyncManager::FireReadyEventsDidFindRegistration,
+                     weak_ptr_factory_.GetWeakPtr(), sw_id_and_key.second,
+                     registration->id(), events_fired_barrier_closure,
+                     events_completed_barrier_closure));
+    }
   }
 
   SchedulePendingRegistrations();
@@ -948,10 +956,11 @@ void BackgroundSyncManager::EventCompleteDidStore(
 
 // static
 void BackgroundSyncManager::OnAllSyncEventsCompleted(
-    const base::TimeTicks& start_time) {
+    const base::TimeTicks& start_time,
+    int number_of_batched_sync_events) {
   // Record the combined time taken by all sync events.
-  BackgroundSyncMetrics::RecordBatchSyncEventHandlingTime(
-      base::TimeTicks::Now() - start_time);
+  BackgroundSyncMetrics::RecordBatchSyncEventComplete(
+      base::TimeTicks::Now() - start_time, number_of_batched_sync_events);
 }
 
 void BackgroundSyncManager::OnRegistrationDeletedImpl(
diff --git a/content/browser/background_sync/background_sync_manager.h b/content/browser/background_sync/background_sync_manager.h
index a235dac..ea0236f 100644
--- a/content/browser/background_sync/background_sync_manager.h
+++ b/content/browser/background_sync/background_sync_manager.h
@@ -267,7 +267,8 @@ class CONTENT_EXPORT BackgroundSyncManager
                              ServiceWorkerStatusCode status_code);
 
   // Called when all sync events have completed.
-  static void OnAllSyncEventsCompleted(const base::TimeTicks& start_time);
+  static void OnAllSyncEventsCompleted(const base::TimeTicks& start_time,
+                                       int number_of_batched_sync_events);
 
   // OnRegistrationDeleted callbacks
   void OnRegistrationDeletedImpl(int64 registration_id,
diff --git a/content/browser/background_sync/background_sync_metrics.cc b/content/browser/background_sync/background_sync_metrics.cc
index 97f20b2..7701798 100644
--- a/content/browser/background_sync/background_sync_metrics.cc
+++ b/content/browser/background_sync/background_sync_metrics.cc
@@ -22,13 +22,16 @@ void BackgroundSyncMetrics::RecordEventResult(SyncPeriodicity periodicity,
   NOTREACHED();
 }
 
-void BackgroundSyncMetrics::RecordBatchSyncEventHandlingTime(
-    const base::TimeDelta& time) {
+void BackgroundSyncMetrics::RecordBatchSyncEventComplete(
+    const base::TimeDelta& time,
+    int number_of_batched_sync_events) {
   // The total batch handling time should be under 5 minutes; we'll record up to
   // 6 minutes, to be safe.
   UMA_HISTOGRAM_CUSTOM_TIMES("BackgroundSync.Event.Time", time,
                              base::TimeDelta::FromMilliseconds(10),
                              base::TimeDelta::FromMinutes(6), 50);
+  UMA_HISTOGRAM_COUNTS_100("BackgroundSync.Event.BatchSize",
+                           number_of_batched_sync_events);
 }
 
 void BackgroundSyncMetrics::CountRegister(
diff --git a/content/browser/background_sync/background_sync_metrics.h b/content/browser/background_sync/background_sync_metrics.h
index 5b74ed5e..290d9f9 100644
--- a/content/browser/background_sync/background_sync_metrics.h
+++ b/content/browser/background_sync/background_sync_metrics.h
@@ -31,8 +31,10 @@ class BackgroundSyncMetrics {
   // Records the result of a single sync event firing.
   static void RecordEventResult(SyncPeriodicity periodicity, bool result);
 
-  // Records the time spent running a batch of sync events.
-  static void RecordBatchSyncEventHandlingTime(const base::TimeDelta& time);
+  // Records the result of running a batch of sync events, including the total
+  // time spent, and the batch size.
+  static void RecordBatchSyncEventComplete(const base::TimeDelta& time,
+                                           int number_of_batched_sync_events);
 
   // Records the result of trying to register a sync. |could_fire| indicates
   // whether the conditions were sufficient for the sync to fire immediately at