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

chrome/browser/signin/chrome_signin_client.cc

 // 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.
 
 #include "chrome/browser/signin/chrome_signin_client.h"
 
 #include "base/command_line.h"
 #include "base/guid.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 44 matching lines @@
 #else
   // UserManager may not exist in unit_tests.
   if (!user_manager::UserManager::IsInitialized())
     return;
 
   const user_manager::User* user =
       chromeos::ProfileHelper::Get()->GetUserByProfile(profile_);
   if (!user)
     return;
   auto* user_manager = user_manager::UserManager::Get();
-  const std::string& user_id = user->GetUserID();
+  const user_manager::UserID& user_id = user->GetUserID();
   if (user_manager->GetKnownUserDeviceId(user_id).empty()) {
     const std::string legacy_device_id =
         GetPrefs()->GetString(prefs::kGoogleServicesSigninScopedDeviceId);
     if (!legacy_device_id.empty()) {
       // Need to move device ID from the old location to the new one, if it has
       // not been done yet.
       user_manager->SetKnownUserDeviceId(user_id, legacy_device_id);
     } else {
       user_manager->SetKnownUserDeviceId(
           user_id,
@@ skipping 239 matching lines @@
   return;
 #else
   // Don't bother if we don't have any kind of network connection.
   if (net::NetworkChangeNotifier::IsOffline()) {
     delayed_callbacks_.push_back(callback);
   } else {
     callback.Run();
   }
 #endif
 }