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

chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h

Index: chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h
diff --git a/chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h b/chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h
index aea7cc03a24d3c05d5255668372acf487a7aa102..2ecaa2a9d99380349231721250da2f94f2db5b2d 100644
--- a/chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h
+++ b/chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h
@@ -19,6 +19,7 @@
 #include "components/ownership/owner_key_util.h"
 #include "components/ownership/owner_settings_service.h"
 #include "components/policy/core/common/cloud/cloud_policy_constants.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
@@ -105,7 +106,7 @@ class OwnerSettingsServiceChromeOS : public ownership::OwnerSettingsService,
   // Assembles PolicyData based on |settings|, |policy_data|, |user_id| and
   // |pending_management_settings|. Applies local-owner policy fixups if needed.
   static scoped_ptr<enterprise_management::PolicyData> AssemblePolicy(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       const enterprise_management::PolicyData* policy_data,
       bool apply_pending_mangement_settings,
       const ManagementSettings& pending_management_settings,
@@ -130,7 +131,7 @@ class OwnerSettingsServiceChromeOS : public ownership::OwnerSettingsService,
   //  1) user whitelisting must be explicitly allowed or disallowed, and
   //  2) the owner user must be on the whitelist, if it's enforced.
   static void FixupLocalOwnerPolicy(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       enterprise_management::ChromeDeviceSettingsProto* settings);
 
   // OwnerSettingsService protected interface overrides:
@@ -168,7 +169,7 @@ class OwnerSettingsServiceChromeOS : public ownership::OwnerSettingsService,
   Profile* profile_;
 
   // User ID this service instance belongs to.
-  std::string user_id_;
+  user_manager::UserID user_id_;
 
   // Whether profile still needs to be initialized.
   bool waiting_for_profile_creation_;