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

chromeos/dbus/utils.h

+// Copyright 2016 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 CHROMEOS_DBUS_UTILS_H_
+#define CHROMEOS_DBUS_UTILS_H_
+
+namespace cryptohome {
+class Identification;
+class AccountIdentifier;
+}
+
+namespace chromeos {
+
+// Fill identification protobuffer.
+void FillIdentificationProtobuf(const cryptohome::Identification& id,
+                                cryptohome::AccountIdentifier* id_proto);
+}  // namespace chromeos
+
+#endif  // CHROMEOS_DBUS_UTILS_H_