This CL replaces user_manager::UserID with AccountId.

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..e57755b99fe938b21b68b57b8a8ff7e7bc093ee7 100644
--- a/chromeos/login/auth/fake_extended_authenticator.cc
+++ b/chromeos/login/auth/fake_extended_authenticator.cc
@@ -6,6 +6,7 @@
 
 #include "base/logging.h"
 #include "chromeos/login/auth/auth_status_consumer.h"
+#include "components/signin/core/account_id/account_id.h"
 
 namespace chromeos {
 
@@ -37,7 +38,8 @@ 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.GetAccountId().GetUserEmail() + "-hash";
     reported_user_context.SetUserIDHash(mount_hash);
     if (!success_callback.is_null())
       success_callback.Run(mount_hash);