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

chromeos/dbus/utils.cc

Index: chromeos/dbus/utils.cc
diff --git a/chromeos/dbus/utils.cc b/chromeos/dbus/utils.cc
new file mode 100644
index 0000000000000000000000000000000000000000..fc2eacdd66577b47341de8a73f3fc5852d05eafa
--- /dev/null
+++ b/chromeos/dbus/utils.cc
@@ -0,0 +1,17 @@
+// 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.
+
+#include "chromeos/dbus/utils.h"
+
+#include "chromeos/cryptohome/cryptohome_parameters.h"
+#include "chromeos/dbus/cryptohome/rpc.pb.h"
+
+namespace chromeos {
+
+void FillIdentificationProtobuf(const cryptohome::Identification& id,
+                                cryptohome::AccountIdentifier* id_proto) {
+  id_proto->set_account_id(id.id());
+}
+
+}  // namespace chromeos