Switch test server to new-style "device gone" status code.

chrome/browser/policy/proto/device_management_backend.proto

 // Copyright (c) 2011 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package enterprise_management;
 
@@ skipping 233 matching lines @@
 // Response from server to device.
 //
 // The server uses the following numbers as HTTP status codes
 // to report top-level errors.
 //
 // 200 OK: valid response is returned to client.
 // 400 Bad Request: invalid argument.
 // 401 Unauthorized: invalid auth cookie or DM token.
 // 403 Forbidden: device management is not allowed.
 // 404 Not Found: the request URL is invalid.
+// 410 Gone: device is unknown to the server.
 // 491 Request Pending: the request is pending approval.
 // 500 Internal Server Error: most likely a bug in DM server.
 // 503 Service Unavailable: most likely a backend error.
 // 901 Device Not Found: the device id is not found.
 // 902 Policy Not Found: the policy is not found.
 message DeviceManagementResponse {
   // Error message.
   optional string error_message = 2;
 
   // Register response
   optional DeviceRegisterResponse register_response = 3;
 
   // Unregister response
   optional DeviceUnregisterResponse unregister_response = 4;
 
   // Policy response.
   optional DevicePolicyResponse policy_response = 5;
 }