Add strings and notifier ID for low disk.

ash/common/system/system_notifier.h

 // Copyright 2013 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_COMMON_SYSTEM_SYSTEM_NOTIFIER_H_
 #define ASH_COMMON_SYSTEM_SYSTEM_NOTIFIER_H_
 
 #include <string>
 
 #include "ash/ash_export.h"
 #include "ui/message_center/notifier_settings.h"
 
 namespace ash {
 namespace system_notifier {
 
 // The list of ash system notifier IDs. Alphabetical order.
 ASH_EXPORT extern const char kNotifierBattery[];
 ASH_EXPORT extern const char kNotifierBluetooth[];
 ASH_EXPORT extern const char kNotifierDeprecatedAccelerator[];
+ASH_EXPORT extern const char kNotifierDisk[];
 ASH_EXPORT extern const char kNotifierDisplay[];
 ASH_EXPORT extern const char kNotifierDisplayResolutionChange[];
 ASH_EXPORT extern const char kNotifierDisplayError[];
 ASH_EXPORT extern const char kNotifierDualRole[];
 ASH_EXPORT extern const char kNotifierHats[];
 ASH_EXPORT extern const char kNotifierLocale[];
 ASH_EXPORT extern const char kNotifierMultiProfileFirstRun[];
 ASH_EXPORT extern const char kNotifierNetwork[];
 ASH_EXPORT extern const char kNotifierNetworkError[];
 ASH_EXPORT extern const char kNotifierNetworkPortalDetector[];
@@ skipping 12 matching lines @@
     const message_center::NotifierId& notifier_id);
 
 // Returns true if |notifier_id| is the system notifier from Ash.
 ASH_EXPORT bool IsAshSystemNotifier(
     const message_center::NotifierId& notifier_id);
 
 }  // namespace system_notifier
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_SYSTEM_NOTIFIER_H_