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

chrome/browser/chromeos/login/existing_user_controller.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_LOGIN_EXISTING_USER_CONTROLLER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_EXISTING_USER_CONTROLLER_H_
 
 #include <stddef.h>
 
 #include <string>
 
 #include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "chrome/browser/chromeos/app_mode/kiosk_app_manager.h"
 #include "chrome/browser/chromeos/login/session/user_session_manager.h"
 #include "chrome/browser/chromeos/login/signin/token_handle_util.h"
 #include "chrome/browser/chromeos/login/ui/login_display.h"
 #include "chrome/browser/chromeos/settings/cros_settings.h"
 #include "chrome/browser/chromeos/settings/device_settings_service.h"
 #include "chromeos/login/auth/login_performer.h"
 #include "chromeos/login/auth/user_context.h"
+#include "components/signin/core/account_id/account_id.h"
 #include "components/user_manager/user.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "ui/gfx/geometry/rect.h"
 #include "url/gurl.h"
 
 namespace base {
 class ListValue;
 }
 
@@ skipping 210 matching lines @@
   void OnTokenHandleChecked(
       const AccountId&,
       TokenHandleUtil::TokenHandleStatus token_handle_status);
 
   // Public session auto-login timer.
   scoped_ptr<base::OneShotTimer> auto_login_timer_;
 
   // Public session auto-login timeout, in milliseconds.
   int public_session_auto_login_delay_;
 
-  // Username for public session auto-login.
-  std::string public_session_auto_login_username_;
+  // AccountId for public session auto-login.
+  AccountId public_session_auto_login_account_id_ = EmptyAccountId();
 
   // Used to execute login operations.
   scoped_ptr<LoginPerformer> login_performer_;
 
   // Delegate to forward all authentication status events to.
   // Tests can use this to receive authentication status events.
   AuthStatusConsumer* auth_status_consumer_ = nullptr;
 
   // AccountId of the last login attempt.
   AccountId last_login_attempt_account_id_ = EmptyAccountId();
@@ skipping 73 matching lines @@
 
   // Factory of callbacks.
   base::WeakPtrFactory<ExistingUserController> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ExistingUserController);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_EXISTING_USER_CONTROLLER_H_