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

chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.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 "chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.h"
 
 #include "base/base64.h"
 #include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
@@ skipping 211 matching lines @@
   std::vector<cryptohome::KeyDefinition> keys;
 
   // Main key is the master key. Just as keys for plain GAIA users, it is salted
   // with system salt. It has all usual privileges.
   cryptohome::KeyDefinition master_key(creation_context_->salted_master_key,
                                        kCryptohomeMasterKeyLabel,
                                        cryptohome::PRIV_DEFAULT);
 
   keys.push_back(master_key);
   authenticator_->CreateMount(
-      creation_context_->local_user_id,
-      keys,
+      AccountId::FromUserEmail(creation_context_->local_user_id), keys,
       base::Bind(&SupervisedUserCreationControllerNew::OnMountSuccess,
                  weak_factory_.GetWeakPtr()));
 }
 
 void SupervisedUserCreationControllerNew::OnAuthenticationFailure(
     ExtendedAuthenticator::AuthState error) {
   timeout_timer_.Stop();
   ErrorCode code = NO_ERROR;
   switch (error) {
     case SupervisedUserAuthenticator::NO_MOUNT:
@@ skipping 171 matching lines @@
   creation_context_->registration_utility.reset();
   chrome::AttemptUserExit();
 }
 
 std::string SupervisedUserCreationControllerNew::GetSupervisedUserId() {
   DCHECK(creation_context_);
   return creation_context_->local_user_id;
 }
 
 }  // namespace chromeos