FIX: notifications not updating correctly from background tab

We refactored some code to avoid app event leak in tests at c462c2f2

Unfortunately this broke all background notifications in title and they
were broken for the past multiple months.

app/assets/javascripts/discourse/initializers/title-notifications.js.es6

@@ -6,8 +6,7 @@ export default {
     const user = container.lookup("current-user:main");
     if (!user) return; // must be logged in
 
-    this.notifications =
-      user.unread_notifications + user.unread_private_messages;
+    this.container = container;
 
     container
       .lookup("app-events:main")
@@ -15,6 +14,12 @@ export default {
   },
 
   _updateTitle() {
-    Discourse.updateNotificationCount(this.notifications);
+    const user = this.container.lookup("current-user:main");
+    if (!user) return; // must be logged in
+
+    const notifications =
+      user.unread_notifications + user.unread_private_messages;
+
+    Discourse.updateNotificationCount(notifications);
   }
 };