Use notification display service to collect persistent notifications.

content/browser/notifications/platform_notification_context_impl.cc

Index: content/browser/notifications/platform_notification_context_impl.cc
diff --git a/content/browser/notifications/platform_notification_context_impl.cc b/content/browser/notifications/platform_notification_context_impl.cc
index fa5c1387e1ccacdb81ebfc43ce707dca5e069afe..775bc9b8f94e610afa34e423280def1190362b70 100644
--- a/content/browser/notifications/platform_notification_context_impl.cc
+++ b/content/browser/notifications/platform_notification_context_impl.cc
@@ -202,6 +202,17 @@ void PlatformNotificationContextImpl::
         const ReadAllResultCallback& callback) {
   DCHECK(task_runner_->RunsTasksOnCurrentThread());
 
+  PlatformNotificationService* service =
+      GetContentClient()->browser()->GetPlatformNotificationService();
+
+  // Ask the underlying implementation what notifications are still being
+  // displayed.
+  std::set<std::string> displayed_notifications;
+  bool notification_synchronization_supported =
+      service &&

[Peter Beverloo, 2016/12/02 13:43:34]

Why would |service| be NULL?

[Miguel Garcia, 2016/12/06 12:01:18]

It's null in some context_unittests like
PlatformNotificationContextTest.ReadAllServiceWorkerDataEmpty

+      service->GetDisplayedPersistentNotifications(browser_context_,
+                                                   &displayed_notifications);
+
   std::vector<NotificationDatabaseData> notification_datas;
 
   NotificationDatabase::Status status =
@@ -212,6 +223,17 @@ void PlatformNotificationContextImpl::
                             status, NotificationDatabase::STATUS_COUNT);
 
   if (status == NotificationDatabase::STATUS_OK) {
+    if (notification_synchronization_supported) {
+      // Filter out notifications that are not actually on display anymore.
+      for (auto it = notification_datas.begin();
+           it != notification_datas.end();) {
+        if (displayed_notifications.count(it->notification_id))
+          ++it;
+        else
+          it = notification_datas.erase(it);
+      }

[Peter Beverloo, 2016/12/02 13:43:34]

We'll want to synchronize the database if there are any inconsistencies. It's
fine to do that as a follow-up, but please add a TODO.

[Miguel Garcia, 2016/12/06 12:01:18]

Done.

+    }
+
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE,
         base::Bind(callback, true /* success */, notification_datas));