ListAccounts will return the Gaia ID as well as the email of the account.

google_apis/gaia/fake_gaia.cc

 // Copyright (c) 2013 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.
 
 #include "google_apis/gaia/fake_gaia.h"
 
 #include <vector>
 
 #include "base/base_paths.h"
 #include "base/bind.h"
@@ skipping 33 matching lines @@
 const char kTestAuthCode[] = "fake-auth-code";
 const char kTestGaiaUberToken[] = "fake-uber-token";
 const char kTestAuthLoginAccessToken[] = "fake-access-token";
 const char kTestRefreshToken[] = "fake-refresh-token";
 const char kTestSessionSIDCookie[] = "fake-session-SID-cookie";
 const char kTestSessionLSIDCookie[] = "fake-session-LSID-cookie";
 const char kTestOAuthLoginSID[] = "fake-oauth-SID-cookie";
 const char kTestOAuthLoginLSID[] = "fake-oauth-LSID-cookie";
 const char kTestOAuthLoginAuthCode[] = "fake-oauth-auth-code";
 
-const char kDefaultGaiaId[]  ="12345";
+const char kDefaultGaiaId[] = "12345";
 
 const base::FilePath::CharType kServiceLogin[] =
     FILE_PATH_LITERAL("google_apis/test/service_login.html");
 
 const base::FilePath::CharType kEmbeddedSetupChromeos[] =
     FILE_PATH_LITERAL("google_apis/test/embedded_setup_chromeos.html");
 
 // OAuth2 Authentication header value prefix.
 const char kAuthHeaderBearer[] = "Bearer ";
 const char kAuthHeaderOAuth[] = "OAuth ";
 
 const char kListAccountsResponseFormat[] =
-    "[\"gaia.l.a.r\",[[\"gaia.l.a\",1,\"\",\"%s\",\"\",1,1,0]]]";
+    "[\"gaia.l.a.r\",[[\"gaia.l.a\",1,\"\",\"%s\",\"\",1,1,0,0,1,\"12345\"]]]";
 
 typedef std::map<std::string, std::string> CookieMap;
 
 // Parses cookie name-value map our of |request|.
 CookieMap GetRequestCookies(const HttpRequest& request) {
   CookieMap result;
   std::map<std::string, std::string>::const_iterator iter =
            request.headers.find("Cookie");
   if (iter != request.headers.end()) {
     std::vector<std::string> cookie_nv_pairs;
@@ skipping 687 matching lines @@
   if (token_info) {
     base::DictionaryValue response_dict;
     response_dict.SetString("id", GetGaiaIdOfEmail(token_info->email));
     response_dict.SetString("email", token_info->email);
     response_dict.SetString("verified_email", token_info->email);
     FormatJSONResponse(response_dict, http_response);
   } else {
     http_response->set_code(net::HTTP_BAD_REQUEST);
   }
 }