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

chrome/browser/chromeos/policy/consumer_management_service.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_CHROMEOS_POLICY_CONSUMER_MANAGEMENT_SERVICE_H_
 #define CHROME_BROWSER_CHROMEOS_POLICY_CONSUMER_MANAGEMENT_SERVICE_H_
 
 #include <string>
 
 #include "base/callback_forward.h"
@@ skipping 92 matching lines @@
   virtual ConsumerManagementStage GetStage() const;
 
   // Sets the stage.
   virtual void SetStage(const ConsumerManagementStage& stage);
 
   // Returns the device owner stored in the boot lockbox via |callback|.
   void GetOwner(const GetOwnerCallback& callback);
 
   // Stores the device owner user ID into the boot lockbox and signs it.
   // |callback| is invoked with an agument indicating success or failure.
-  void SetOwner(const std::string& user_id, const SetOwnerCallback& callback);
+  void SetOwner(const user_manager::UserID& user_id, const SetOwnerCallback& callback);
 
   // chromeos::DeviceSettingsService::Observer:
   void OwnershipStatusChanged() override;
   void DeviceSettingsUpdated() override;
   void OnDeviceSettingsServiceShutdown() override;
 
  protected:
   void NotifyStatusChanged();
 
  private:
@@ skipping 19 matching lines @@
 
   ObserverList<Observer, true> observers_;
   base::WeakPtrFactory<ConsumerManagementService> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ConsumerManagementService);
 };
 
 }  // namespace policy
 
 #endif  // CHROME_BROWSER_CHROMEOS_POLICY_CONSUMER_MANAGEMENT_SERVICE_H_