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

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.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 "chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <vector>
@@ skipping 970 matching lines @@
     return;
   DCHECK_EQ(account_id.GetUserEmail(),
             gaia::SanitizeEmail(account_id.GetUserEmail()));
 
   UserContext user_context(account_id);
   user_context.SetKey(Key(password));
   delegate_->Login(user_context, SigninSpecifics());
 }
 
 void SigninScreenHandler::HandleLaunchIncognito() {
-  UserContext context(user_manager::USER_TYPE_GUEST, std::string());
+  UserContext context(user_manager::USER_TYPE_GUEST, EmptyAccountId());
   if (delegate_)
     delegate_->Login(context, SigninSpecifics());
 }
 
 void SigninScreenHandler::HandleShowSupervisedUserCreationScreen() {
   if (!user_manager::UserManager::Get()->AreSupervisedUsersAllowed()) {
     LOG(ERROR) << "Managed users not allowed.";
     return;
   }
   LoginDisplayHost::default_host()->StartWizard(
       WizardController::kSupervisedUserCreationScreenName);
 }
 
 void SigninScreenHandler::HandleLaunchPublicSession(
     const AccountId& account_id,
     const std::string& locale,
     const std::string& input_method) {
   if (!delegate_)
     return;
 
-  UserContext context(user_manager::USER_TYPE_PUBLIC_ACCOUNT,
-                      account_id.GetUserEmail());
+  UserContext context(user_manager::USER_TYPE_PUBLIC_ACCOUNT, account_id);
   context.SetPublicSessionLocale(locale),
   context.SetPublicSessionInputMethod(input_method);
   delegate_->Login(context, SigninSpecifics());
 }
 
 void SigninScreenHandler::HandleOfflineLogin(const base::ListValue* args) {
   if (!delegate_ || delegate_->IsShowUsers()) {
     NOTREACHED();
     return;
   }
@@ skipping 232 matching lines @@
 void SigninScreenHandler::SendPublicSessionKeyboardLayouts(
     const AccountId& account_id,
     const std::string& locale,
     scoped_ptr<base::ListValue> keyboard_layouts) {
   CallJS("login.AccountPickerScreen.setPublicSessionKeyboardLayouts",
          account_id, locale, *keyboard_layouts);
 }
 
 void SigninScreenHandler::HandleLaunchKioskApp(const AccountId& app_account_id,
                                                bool diagnostic_mode) {
-  UserContext context(user_manager::USER_TYPE_KIOSK_APP,
-                      app_account_id.GetUserEmail());
+  UserContext context(user_manager::USER_TYPE_KIOSK_APP, app_account_id);
   SigninSpecifics specifics;
   specifics.kiosk_diagnostic_mode = diagnostic_mode;
   if (delegate_)
     delegate_->Login(context, specifics);
 }
 
 void SigninScreenHandler::HandleGetTouchViewState() {
   if (max_mode_delegate_) {
     CallJS("login.AccountPickerScreen.setTouchViewState",
            max_mode_delegate_->IsMaximizeModeEnabled());
@@ skipping 108 matching lines @@
   return gaia_screen_handler_->frame_error();
 }
 
 void SigninScreenHandler::OnCapsLockChanged(bool enabled) {
   caps_lock_enabled_ = enabled;
   if (page_is_ready())
     CallJS("login.AccountPickerScreen.setCapsLockState", caps_lock_enabled_);
 }
 
 }  // namespace chromeos