Extract the view of control buttons on notification into a separated class

ui/arc/notification/arc_notification_delegate.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 UI_ARC_NOTIFICATION_ARC_CUSTOM_DELEGATE_H_
 #define UI_ARC_NOTIFICATION_ARC_CUSTOM_DELEGATE_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "ui/message_center/notification_delegate.h"
@@ skipping 14 matching lines @@
 class ArcNotificationDelegate : public message_center::NotificationDelegate {
  public:
   explicit ArcNotificationDelegate(base::WeakPtr<ArcNotificationItem> item);
 
   // message_center::NotificationDelegate overrides:
   std::unique_ptr<message_center::MessageView> CreateCustomMessageView(
       message_center::MessageCenterController* controller,
       const message_center::Notification& notification) override;
   void Close(bool by_user) override;
   void Click() override;
+  bool SettingsClick() override;
 
  private:
   // The destructor is private since this class is ref-counted.
   ~ArcNotificationDelegate() override;
 
   // We use weak ptr to detect potential use-after-free. The lives of objects
   // around ARC notification is somewhat complex so we want to use it until
   // it gets stable.
   base::WeakPtr<ArcNotificationItem> item_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcNotificationDelegate);
 };
 
 }  // namespace arc
 
 #endif  // UI_ARC_NOTIFICATION_ARC_CUSTOM_DELEGATE_H_