Make GetDisplayedNotifications asynchronous.

chrome/browser/notifications/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_NOTIFICATION_PLATFORM_BRIDGE_H_
 #define CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_PLATFORM_BRIDGE_H_
 
 #include <set>
 #include <string>
 
+#include "base/callback_forward.h"
 #include "base/macros.h"
 #include "chrome/browser/notifications/notification_common.h"
 
 class Notification;
 
 // Provides the low-level interface that enables notifications to be displayed
 // and interacted with on the user's screen, orthogonal of whether this
 // functionality is provided by the browser or by the operating system.
 // TODO(miguelg): Add support for click and close events.
 class NotificationPlatformBridge {
  public:
+  using DisplayedNotificationsCallback =
+      base::Callback<void(std::unique_ptr<std::set<std::string>>,
+                          bool /* supports_synchronization */)>;
+
   static NotificationPlatformBridge* Create();
 
   virtual ~NotificationPlatformBridge() {}
 
   // Shows a toast on screen using the data passed in |notification|.
   virtual void Display(NotificationCommon::Type notification_type,
                        const std::string& notification_id,
                        const std::string& profile_id,
                        bool is_incognito,
                        const Notification& notification) = 0;
 
   // Closes a nofication with |notification_id| and |profile_id| if being
   // displayed.
   virtual void Close(const std::string& profile_id,
                      const std::string& notification_id) = 0;
 
-  // Fills in |notifications| with a set of notification ids currently being
-  // displayed for a given profile.
-  // The return value expresses whether the underlying platform has the
-  // capability to provide displayed notifications so the empty set
-  // can be disambiguated.
-  virtual bool GetDisplayed(const std::string& profile_id,
-                            bool incognito,
-                            std::set<std::string>* notification_ids) const = 0;
+  // Writes the ids of all currently displaying notifications and posts
+  // |callback| with the result.
+  virtual void GetDisplayed(
+      const std::string& profile_id,
+      bool incognito,
+      const DisplayedNotificationsCallback& callback) const = 0;
 
  protected:
   NotificationPlatformBridge() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NotificationPlatformBridge);
 };
 
 #endif  // CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_PLATFORM_BRIDGE_H_