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

chrome/browser/chromeos/settings/device_settings_service.h

Index: chrome/browser/chromeos/settings/device_settings_service.h
diff --git a/chrome/browser/chromeos/settings/device_settings_service.h b/chrome/browser/chromeos/settings/device_settings_service.h
index 34c99b713a461fd20622cbfb66c19241eb1bb928..0d9f7887c6a7053cc5684c7838d7f4dc21fb5bb9 100644
--- a/chrome/browser/chromeos/settings/device_settings_service.h
+++ b/chrome/browser/chromeos/settings/device_settings_service.h
@@ -20,6 +20,7 @@
 #include "chromeos/dbus/session_manager_client.h"
 #include "components/ownership/owner_settings_service.h"
 #include "components/policy/core/common/cloud/cloud_policy_validator.h"
+#include "components/user_manager/user_id.h"
 #include "crypto/scoped_nss_types.h"
 #include "policy/proto/device_management_backend.pb.h"
 
@@ -160,11 +161,11 @@ class DeviceSettingsService : public SessionManagerClient::Observer {
   // write path for device settings will be removed from
   // DeviceSettingsProvider and all existing clients will be switched
   // to OwnerSettingsServiceChromeOS.
-  void InitOwner(const std::string& username,
+  void InitOwner(const user_manager::UserID& user_id,
                  const base::WeakPtr<ownership::OwnerSettingsService>&
                      owner_settings_service);
 
-  const std::string& GetUsername() const;
+  const user_manager::UserID& GetUserID() const;
 
   ownership::OwnerSettingsService* GetOwnerSettingsService() const;
 
@@ -210,7 +211,7 @@ class DeviceSettingsService : public SessionManagerClient::Observer {
 
   std::vector<OwnershipStatusCallback> pending_ownership_status_callbacks_;
 
-  std::string username_;
+  user_manager::UserID user_id_;
   scoped_refptr<ownership::PublicKey> public_key_;
   base::WeakPtr<ownership::OwnerSettingsService> owner_settings_service_;