[BackgroundSync]: Resolve the register promise before firing sync events

content/browser/background_sync/background_sync_manager.cc

Index: content/browser/background_sync/background_sync_manager.cc
diff --git a/content/browser/background_sync/background_sync_manager.cc b/content/browser/background_sync/background_sync_manager.cc
index 97ba87a7e522916fdb14951138adeb80a658b34d..cad67586a526872c259fea3b4ab2e8f7c64175e4 100644
--- a/content/browser/background_sync/background_sync_manager.cc
+++ b/content/browser/background_sync/background_sync_manager.cc
@@ -687,13 +687,13 @@ void BackgroundSyncManager::RegisterDidStore(
       registration_could_fire,
       BackgroundSyncMetrics::REGISTRATION_IS_NOT_DUPLICATE);
 
-  FireReadyEvents();
-
-  base::ThreadTaskRunnerHandle::Get()->PostTask(
+  base::ThreadTaskRunnerHandle::Get()->PostTaskAndReply(
       FROM_HERE,
       base::Bind(callback, BACKGROUND_SYNC_STATUS_OK,
                  base::Passed(base::MakeUnique<BackgroundSyncRegistration>(
-                     new_registration))));
+                     new_registration))),
+      base::Bind(&BackgroundSyncManager::FireReadyEvents,
+                 weak_ptr_factory_.GetWeakPtr()));
 }
 
 void BackgroundSyncManager::RemoveActiveRegistration(int64_t sw_registration_id,