Add Ash notification UI for OutOfCredits network property

ash/system/chromeos/network/network_observer.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_OBSERVER_H
 #define ASH_SYSTEM_CHROMEOS_NETWORK_NETWORK_OBSERVER_H
 
 #include <vector>
 
 #include "base/string16.h"
 
 namespace ash {
 
 struct NetworkIconInfo;
-
-class NetworkTrayDelegate {
- public:
-  virtual ~NetworkTrayDelegate() {}
-
-  // Notifies that the |index|-th link on the notification is clicked.
-  virtual void NotificationLinkClicked(size_t index) = 0;
-};
+class NetworkTrayDelegate;
 
 class NetworkObserver {
  public:
   enum MessageType {
     // Priority order, highest to lowest.
     ERROR_CONNECT_FAILED,
+    ERROR_OUT_OF_CREDITS,
     MESSAGE_DATA_PROMO,
   };
 
   enum NetworkType {
     // ash relevant subset of network_constants.h connection type.
     NETWORK_ETHERNET,
     NETWORK_CELLULAR,
     NETWORK_CELLULAR_LTE,
     NETWORK_WIFI,
     NETWORK_BLUETOOTH,
@@ skipping 20 matching lines @@
 
   // Called when the user attempted to toggle Wi-Fi enable/disable.
   // NOTE: Toggling is asynchronous and subsequent calls to query the current
   // state may return the old value.
   virtual void OnWillToggleWifi() = 0;
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_NETWORK_NETWORK_OBSERVER_H