Implement TOGGLE_EXPANSION action for the ARC notifications.

ui/arc/notification/arc_notification_manager.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 UI_ARC_NOTIFICATION_ARC_NOTIFICATION_MANAGER_H_
 #define UI_ARC_NOTIFICATION_ARC_NOTIFICATION_MANAGER_H_
 
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ skipping 36 matching lines @@
 
   // Methods called from ArcNotificationItem:
   void SendNotificationRemovedFromChrome(const std::string& key);
   void SendNotificationClickedOnChrome(const std::string& key);
   void SendNotificationButtonClickedOnChrome(const std::string& key,
                                              int button_index);
   void CreateNotificationWindow(const std::string& key);
   void CloseNotificationWindow(const std::string& key);
   void OpenNotificationSettings(const std::string& key);
   bool IsOpeningSettingsSupported() const;
+  void SendNotificationToggleExpansionOnChrome(const std::string& key);
 
  private:
   const AccountId main_profile_id_;
   message_center::MessageCenter* const message_center_;
 
   using ItemMap =
       std::unordered_map<std::string, std::unique_ptr<ArcNotificationItem>>;
   ItemMap items_;
 
   bool ready_ = false;
 
   mojo::Binding<mojom::NotificationsHost> binding_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcNotificationManager);
 };
 
 }  // namespace arc
 
 #endif  // UI_ARC_NOTIFICATION_ARC_NOTIFICATION_MANAGER_H_