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

chromeos/login/auth/fake_extended_authenticator.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 "chromeos/login/auth/fake_extended_authenticator.h"
 
 #include "base/logging.h"
 #include "chromeos/login/auth/auth_status_consumer.h"
 #include "components/signin/core/account_id/account_id.h"
 
@@ skipping 47 matching lines @@
     if (!success_callback.is_null())
       success_callback.Run();
     OnAuthSuccess(context);
     return;
   }
 
   OnAuthFailure(FAILED_MOUNT,
                 AuthFailure(AuthFailure::UNLOCK_FAILED));
 }
 
-void FakeExtendedAuthenticator::CreateMount(const std::string& user_id,
-                         const std::vector<cryptohome::KeyDefinition>& keys,
-                         const ResultCallback& success_callback) {
+void FakeExtendedAuthenticator::CreateMount(
+    const AccountId& account_id,
+    const std::vector<cryptohome::KeyDefinition>& keys,
+    const ResultCallback& success_callback) {
   NOTREACHED();
 }
 
 void FakeExtendedAuthenticator::AddKey(const UserContext& context,
                     const cryptohome::KeyDefinition& key,
                     bool replace_existing,
                     const base::Closure& success_callback) {
   NOTREACHED();
 }
 
@@ skipping 25 matching lines @@
 
 void FakeExtendedAuthenticator::OnAuthFailure(AuthState state,
                                               const AuthFailure& error) {
   if (consumer_)
     consumer_->OnAuthenticationFailure(state);
   if (old_consumer_)
     old_consumer_->OnAuthFailure(error);
 }
 
 }  // namespace chromeos