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

chromeos/login/auth/stub_authenticator.cc

Index: chromeos/login/auth/stub_authenticator.cc
diff --git a/chromeos/login/auth/stub_authenticator.cc b/chromeos/login/auth/stub_authenticator.cc
index 371453d8f8a0a871f70b67ce70ede31598488d92..d48d59648ff8b9b59fbe3efb763b764e172ad301 100644
--- a/chromeos/login/auth/stub_authenticator.cc
+++ b/chromeos/login/auth/stub_authenticator.cc
@@ -75,7 +75,7 @@ void StubAuthenticator::LoginAsPublicSession(const UserContext& user_context) {
 }
 
 void StubAuthenticator::LoginAsKioskAccount(
-    const std::string& /* app_user_id */,
+    const AccountId& /* app_account_id */,
     bool use_guest_mount) {
   UserContext user_context(expected_user_context_.GetAccountId());
   user_context.SetIsUsingOAuth(false);