Make GetDisplayedNotifications asynchronous.

chrome/browser/notifications/stub_notification_platform_bridge.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_NOTIFICATIONS_STUB_NOTIFICATION_PLATFORM_BRIDGE_H_
 #define CHROME_BROWSER_NOTIFICATIONS_STUB_NOTIFICATION_PLATFORM_BRIDGE_H_
 
 #include <unordered_map>
 #include <vector>
 
 #include "base/macros.h"
 #include "chrome/browser/notifications/notification.h"
 #include "chrome/browser/notifications/notification_common.h"
 #include "chrome/browser/notifications/notification_platform_bridge.h"
 
 // Implementation of NotificationPlatformBridge used for tests.
 class StubNotificationPlatformBridge : public NotificationPlatformBridge {
  public:
   StubNotificationPlatformBridge();
   ~StubNotificationPlatformBridge() override;
 
   // Returns the notification being displayed at position |index|.
   Notification GetNotificationAt(std::string profile_id, size_t index);
 
+  // Returns the number of notifications displayed.
+  size_t GetNotificationCount();
+
   // NotificationPlatformBridge implementation.
   void Display(NotificationCommon::Type notification_type,
                const std::string& notification_id,
                const std::string& profile_id,
                bool incognito,
                const Notification& notification) override;
   void Close(const std::string& profile_id,
              const std::string& notification_id) override;
-  bool GetDisplayed(const std::string& profile_id,
-                    bool incognito,
-                    std::set<std::string>* notifications) const override;
+  void GetDisplayed(
+      const std::string& profile_id,
+      bool incognito,
+      const DisplayedNotificationsCallback& callback) const override;
 
  private:
   // Map of profile Ids to list of notifications shown for said profile.
   std::unordered_map<std::string, std::vector<Notification>> notifications_;
 
   DISALLOW_COPY_AND_ASSIGN(StubNotificationPlatformBridge);
 };
 
 #endif  // CHROME_BROWSER_NOTIFICATIONS_STUB_NOTIFICATION_PLATFORM_BRIDGE_H_