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

chromeos/login/auth/utils.h

Index: chromeos/login/auth/utils.h
diff --git a/chromeos/login/auth/utils.h b/chromeos/login/auth/utils.h
new file mode 100644
index 0000000000000000000000000000000000000000..dddecbd2421076026c0ac14ac578a8f7ec0d04d3
--- /dev/null
+++ b/chromeos/login/auth/utils.h
@@ -0,0 +1,19 @@
+// 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_LOGIN_AUTH_UTILS_H_
+#define CHROMEOS_LOGIN_AUTH_UTILS_H_
+
+#include "chromeos/chromeos_export.h"
+
+class AccountId;
+
+namespace cryptohome {
+class Identification;
+
+// Lookup AccountId matching given Identification.
+CHROMEOS_EXPORT AccountId GetAccountId(const Identification& user_id);
+}  // namespace cryptohome
+
+#endif  // CHROMEOS_LOGIN_AUTH_UTILS_H_