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

chromeos/login/auth/fake_extended_authenticator.cc

Index: chromeos/login/auth/fake_extended_authenticator.cc
diff --git a/chromeos/login/auth/fake_extended_authenticator.cc b/chromeos/login/auth/fake_extended_authenticator.cc
index e57755b99fe938b21b68b57b8a8ff7e7bc093ee7..b44255b5bbc7e7bb6a70700a3f7b989843f3c72d 100644
--- a/chromeos/login/auth/fake_extended_authenticator.cc
+++ b/chromeos/login/auth/fake_extended_authenticator.cc
@@ -65,9 +65,10 @@ void FakeExtendedAuthenticator::AuthenticateToCheck(
                 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();
 }