Extract common per-network proxy configuration functions.

chromeos/network/network_handler_callbacks.h

Index: chromeos/network/network_handler_callbacks.h
diff --git a/chromeos/network/network_handler_callbacks.h b/chromeos/network/network_handler_callbacks.h
index 8caf804e0a94aac655e7fb08b59f52744fa76284..2e73d2810bf4d8363fd6081ed4a91f65285e505b 100644
--- a/chromeos/network/network_handler_callbacks.h
+++ b/chromeos/network/network_handler_callbacks.h
@@ -39,10 +39,11 @@ CHROMEOS_EXPORT base::DictionaryValue* CreateErrorData(
 
 // Callback for Shill errors. |path| may be blank if not relevant.
 // Logs an error and calls |error_callback| if not null.
-void ShillErrorCallbackFunction(const std::string& path,
-                                const ErrorCallback& error_callback,
-                                const std::string& error_name,
-                                const std::string& error_message);
+CHROMEOS_EXPORT void ShillErrorCallbackFunction(
+    const std::string& path,
+    const ErrorCallback& error_callback,
+    const std::string& error_name,
+    const std::string& error_message);
 
 }  // namespace network_handler
 }  // namespace chromeos