Part 1 of work to do user sign in based on OAuth2:

chrome/common/net/gaia/google_service_auth_error.h

 // 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.
 
 // A GoogleServiceAuthError is immutable, plain old data representing an
 // error from an attempt to authenticate with a Google service.
 // It could be from Google Accounts itself, or any service using Google
 // Accounts (e.g expired credentials).  It may contain additional data such as
 // captcha challenges.
 
@@ skipping 60 matching lines @@
     // The password is valid but we need two factor to get a token.
     TWO_FACTOR = 8,
 
     // The requestor of the authentication step cancelled the request
     // prior to completion.
     REQUEST_CANCELED = 9,
 
     // The user has provided a HOSTED account, when this service requires
     // a GOOGLE account.
     HOSTED_NOT_ALLOWED = 10,
+
+    // Response format was unexpected.
+    UNEXPECTED_RESPONSE = 11,
   };
 
   // Additional data for CAPTCHA_REQUIRED errors.
   struct Captcha {
     Captcha(const std::string& t, const GURL& img, const GURL& unlock);
     std::string token;  // Globally identifies the specific CAPTCHA challenge.
     GURL image_url;     // The CAPTCHA image to show the user.
     GURL unlock_url;    // Pretty unlock page containing above captcha.
   };
 
@@ skipping 33 matching lines @@
   GoogleServiceAuthError(State s, const std::string& captcha_token,
                          const GURL& captcha_image_url,
                          const GURL& captcha_unlock_url);
 
   State state_;
   Captcha captcha_;
   int network_error_;
 };
 
 #endif  // CHROME_COMMON_NET_GAIA_GOOGLE_SERVICE_AUTH_ERROR_H_