Mark create/update/clear callbacks of notification API as optional

chrome/browser/extensions/api/notifications/notifications_api.cc

Index: chrome/browser/extensions/api/notifications/notifications_api.cc
diff --git a/chrome/browser/extensions/api/notifications/notifications_api.cc b/chrome/browser/extensions/api/notifications/notifications_api.cc
index 3830a7cf3358656bc3cd5745470456688d1350d0..26ee99e1476b8054441f6119dd6854e2a7ef7d18 100644
--- a/chrome/browser/extensions/api/notifications/notifications_api.cc
+++ b/chrome/browser/extensions/api/notifications/notifications_api.cc
@@ -477,9 +477,9 @@ bool NotificationsCreateFunction::RunNotificationsApi() {
 
   const std::string extension_id(extension_->id());
   std::string notification_id;
-  if (!params_->notification_id.empty()) {
+  if (params_->notification_id.get() && !params_->notification_id->empty()) {
     // If the caller provided a notificationId, use that.
-    notification_id = params_->notification_id;
+    notification_id = *params_->notification_id;
   } else {
     // Otherwise, use a randomly created GUID. In case that GenerateGUID returns
     // the empty string, simply generate a random string.