[Mac] Add XPC alerts to GetDisplayedNotifications

chrome/browser/notifications/displayed_notifications_dispatch_callback.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_NOTIFICATIONS_DISPLAYED_NOTIFICATIONS_DISPATCH_CALLBACK_H_
+#define CHROME_BROWSER_NOTIFICATIONS_DISPLAYED_NOTIFICATIONS_DISPATCH_CALLBACK_H_
+
+#include "base/callback.h"
+
+// Callback used by the bridge and all the downstream classes that propagate
+// the callback to get displayed notifications.
+using GetDisplayedNotificationsCallback =
+    base::Callback<void(std::unique_ptr<std::set<std::string>>,
+                        bool /* supports_synchronization */)>;
+
+#endif  // CHROME_BROWSER_NOTIFICATIONS_DISPLAYED_NOTIFICATIONS_DISPATCH_CALLBACK_H_