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

components/user_manager.gypi

 # 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.
 
 {
   'variables': {
     # Cross-platform user_manager sources.
     'user_manager_shared_sources': [
       'user_manager/empty_user_info.cc',
       'user_manager/empty_user_info.h',
+      'user_manager/user_id.cc',
       'user_manager/user_id.h',
       'user_manager/user_info.cc',
       'user_manager/user_info.h',
       'user_manager/user_info_impl.cc',
       'user_manager/user_info_impl.h',
       'user_manager/user_manager_export.h',
     ],
     # Chrome OS user_manager sources.
     'user_manager_chromeos_sources': [
       'user_manager/remove_user_delegate.h',
@@ skipping 57 matching lines @@
           'user_manager',
         ],
         'sources': [
           'user_manager/fake_user_manager.cc',
           'user_manager/fake_user_manager.h',
         ],
       }],
      ]
   },],
 }