We should use UserID object to identify users instead of username.

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 90b569bc13d4ed697405a1b8f366211caa1052ab..b905524d7a1e308730dd32094ff462a81ba696c2 100644
--- a/chromeos/login/auth/fake_extended_authenticator.cc
+++ b/chromeos/login/auth/fake_extended_authenticator.cc
@@ -37,7 +37,7 @@ void FakeExtendedAuthenticator::AuthenticateToMount(
     const ResultCallback& success_callback) {
   if (expected_user_context_ == context) {
     UserContext reported_user_context(context);
-    const std::string mount_hash = reported_user_context.GetUserID() + "-hash";
+    const std::string mount_hash = reported_user_context.GetUserID().GetUserEmail() + "-hash";
     reported_user_context.SetUserIDHash(mount_hash);
     if (!success_callback.is_null())
       success_callback.Run(mount_hash);
@@ -63,7 +63,7 @@ void FakeExtendedAuthenticator::AuthenticateToCheck(
                 AuthFailure(AuthFailure::UNLOCK_FAILED));
 }
 
-void FakeExtendedAuthenticator::CreateMount(const std::string& user_id,
+void FakeExtendedAuthenticator::CreateMount(const user_manager::UserID& user_id,
                          const std::vector<cryptohome::KeyDefinition>& keys,
                          const ResultCallback& success_callback) {
   NOTREACHED();