tray: Show warning in network tray when VPN or proxy used.

ash/system/networking_config_delegate.h

 // Copyright 2015 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_NETWORKING_CONFIG_DELEGATE_H_
 #define ASH_SYSTEM_NETWORKING_CONFIG_DELEGATE_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 20 matching lines @@
     std::string extension_name;
   };
 
   virtual ~NetworkingConfigDelegate() {}
 
   // Returns information about the extension registered to control configuration
   // of the network |guid|. Returns null if no extension is registered.
   virtual std::unique_ptr<const ExtensionInfo> LookUpExtensionForNetwork(
       const std::string& guid) = 0;
 
+  virtual bool HasDefaultNetworkProxyConfigured() = 0;
+
  private:
   DISALLOW_ASSIGN(NetworkingConfigDelegate);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_NETWORKING_CONFIG_DELEGATE_H_