Make GetDisplayedNotifications asynchronous.

chrome/browser/ui/cocoa/notifications/notification_delivery.h

 // Copyright 2016 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_UI_COCOA_NOTIFICATIONS_NOTIFICATION_DELIVERY_H_
 #define CHROME_BROWSER_UI_COCOA_NOTIFICATIONS_NOTIFICATION_DELIVERY_H_
 
 #import <Foundation/Foundation.h>
 
 #import "chrome/browser/ui/cocoa/notifications/xpc_mach_port.h"
 
 // Collection of protocols used for XPC communication between chrome
 // and the alert notification xpc service.
 
 // Protocol for the XPC notification service.
 @protocol NotificationDelivery
 
 // Sets the Mach exception handler port to use for the XPCService.
 - (void)setMachExceptionPort:(CrXPCMachPort*)port;
 
 // |notificationData| is generated using a NofiticationBuilder object.
 - (void)deliverNotification:(NSDictionary*)notificationData;
 
 // Closes an alert with the given |notificationId| and |profileId|.
 - (void)closeNotificationWithId:(NSString*)notificationId
                   withProfileId:(NSString*)profileId;
 
 // Closes all the alerts being displayed.
 - (void)closeAllNotifications;
-
 @end
 
 // Response protocol for the XPC notification service to notify Chrome of
 // notification interactions.
 @protocol NotificationReply
 
 // |notificationResponseData| is generated through a
 // NotificationResponseBuilder.
 - (void)notificationClick:(NSDictionary*)notificationResponseData;
 
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_NOTIFICATIONS_NOTIFICATION_DELIVERY_H_