Add Ash notification UI for OutOfCredits network property

ash/system/chromeos/network/network_tray_delegate.h

+// Copyright (c) 2012 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 ASH_SYSTEM_CHROMEOS_NETWORK_NETWORK_TRAY_DELEGATE_H
+#define ASH_SYSTEM_CHROMEOS_NETWORK_NETWORK_TRAY_DELEGATE_H
+
+#include "ash/system/chromeos/network/network_observer.h"
+
+namespace ash {
+
+class NetworkTrayDelegate {
+ public:
+  virtual ~NetworkTrayDelegate() {}
+
+  // Notifies that the |index|-th link on the notification is clicked.
+  virtual void NotificationLinkClicked(
+      NetworkObserver::MessageType message_type,
+      size_t link_index) = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_CHROMEOS_NETWORK_NETWORK_TRAY_DELEGATE_H