Add NetworkNotificationView to tray_network.

ash/system/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_NETWORK_NETWORK_OBSERVER_H
 #define ASH_SYSTEM_NETWORK_NETWORK_OBSERVER_H
 #pragma once
 
+#include "base/string16.h"
+
 namespace ash {
 
 struct NetworkIconInfo;
+class NetworkTrayDelegate;
+
+class NetworkTrayDelegate {
+ public:
+  virtual ~NetworkTrayDelegate() {}
+
+  virtual void NotificationLinkClicked() = 0;
+};
 
 class NetworkObserver {
  public:
+  enum ErrorType {
+    // Priority order, highest to lowest.
+    ERROR_CONNECT_FAILED,
+    ERROR_DATA_NONE,
+    ERROR_DATA_LOW
+  };
+
   virtual ~NetworkObserver() {}
 
   virtual void OnNetworkRefresh(const NetworkIconInfo& info) = 0;
+
+  // Sets a network error notification. |error_type| identifies the type of
+  // error. |delegate|->NotificationLinkClicked() will be called if |link_text|
+  // is clicked (if supplied, |link_text| may be empty).
+  virtual void SetNetworkError(NetworkTrayDelegate* delegate,
+                               ErrorType error_type,
+                               const string16& title,
+                               const string16& message,
+                               const string16& link_text) = 0;
+  // Clears the error notification for |error_type|.
+  virtual void ClearNetworkError(ErrorType error_type) = 0;
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_NETWORK_NETWORK_OBSERVER_H