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

ui/arc/notification/arc_notification_delegate.cc

 // 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.
 
 #include "ui/arc/notification/arc_notification_delegate.h"
 
 #include "ui/arc/notification/arc_notification_content_view.h"
 #include "ui/arc/notification/arc_notification_item.h"
 #include "ui/arc/notification/arc_notification_view.h"
 #include "ui/message_center/notification.h"
@@ skipping 27 matching lines @@
 void ArcNotificationDelegate::Close(bool by_user) {
   DCHECK(item_);
   item_->Close(by_user);
 }
 
 void ArcNotificationDelegate::Click() {
   DCHECK(item_);
   item_->Click();
 }
 
+bool ArcNotificationDelegate::SettingsClick() {
+  DCHECK(item_);
+  item_->OpenSettings();
+  return true;
+}
+
 }  // namespace arc