ChromeOS cryptohome should be able to use gaia id as user identifier.

chrome/browser/chromeos/login/signin/oauth2_browsertest.cc

 // Copyright 2014 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 <string>
 #include <utility>
 
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/stringprintf.h"
@@ skipping 246 matching lines @@
   bool AddUserToSession(const AccountId& account_id,
                         const std::string& password) {
     ExistingUserController* controller =
         ExistingUserController::current_controller();
     if (!controller) {
       ADD_FAILURE();
       return false;
     }
 
     UserContext user_context(account_id);
-    user_context.SetGaiaID(account_id.GetGaiaId());
     user_context.SetKey(Key(password));
     controller->Login(user_context, SigninSpecifics());
     content::WindowedNotificationObserver(
         chrome::NOTIFICATION_SESSION_STARTED,
         content::NotificationService::AllSources()).Wait();
     const user_manager::UserList& logged_users =
         user_manager::UserManager::Get()->GetLoggedInUsers();
     for (user_manager::UserList::const_iterator it = logged_users.begin();
          it != logged_users.end();
          ++it) {
@@ skipping 528 matching lines @@
 
   if (!catcher.GetNextResult()) {
     std::string message = catcher.message();
     ADD_FAILURE() << "Tests failed: " << message;
   }
 
   EXPECT_TRUE(fake_google_.IsPageRequested());
 }
 
 }  // namespace chromeos