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

chrome/browser/signin/easy_unlock_auth_attempt.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/easy_unlock_auth_attempt.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "chrome/browser/signin/easy_unlock_app_manager.h"
 #include "chrome/browser/signin/proximity_auth_facade.h"
@@ skipping 30 matching lines @@
   std::string secret;
   if (!encryptor.Decrypt(wrapped_secret, &secret))
     return std::string();
 
   return secret;
 }
 
 void DefaultAuthAttemptFinalizedHandler(
     EasyUnlockAuthAttempt::Type auth_attempt_type,
     bool success,
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     const std::string& key_secret,
     const std::string& key_label) {
   if (!GetScreenlockBridgeInstance()->IsLocked())
     return;
 
   switch (auth_attempt_type) {
     case EasyUnlockAuthAttempt::TYPE_UNLOCK:
       if (success) {
         GetScreenlockBridgeInstance()->lock_handler()->Unlock(user_id);
       } else {
@@ skipping 11 matching lines @@
             user_id, std::string(), std::string());
       }
       return;
   }
 }
 
 }  // namespace
 
 EasyUnlockAuthAttempt::EasyUnlockAuthAttempt(
     EasyUnlockAppManager* app_manager,
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     Type type,
     const FinalizedCallback& finalized_callback)
     : app_manager_(app_manager),
       state_(STATE_IDLE),
       user_id_(user_id),
       type_(type),
       finalized_callback_(finalized_callback) {
   if (finalized_callback_.is_null())
     finalized_callback_ = base::Bind(&DefaultAuthAttemptFinalizedHandler);
 }
@@ skipping 20 matching lines @@
   state_ = STATE_RUNNING;
 
   if (!app_manager_->SendAuthAttemptEvent()) {
     Cancel(user_id_);
     return false;
   }
 
   return true;
 }
 
-void EasyUnlockAuthAttempt::FinalizeUnlock(const std::string& user_id,
+void EasyUnlockAuthAttempt::FinalizeUnlock(const user_manager::UserID& user_id,
                                            bool success) {
   if (state_ != STATE_RUNNING || user_id != user_id_)
     return;
 
   if (!GetScreenlockBridgeInstance()->IsLocked())
     return;
 
   if (type_ != TYPE_UNLOCK) {
     Cancel(user_id_);
     return;
   }
 
   finalized_callback_.Run(type_, success, user_id, std::string(),
                           std::string());
   state_ = STATE_DONE;
 }
 
-void EasyUnlockAuthAttempt::FinalizeSignin(const std::string& user_id,
+void EasyUnlockAuthAttempt::FinalizeSignin(const user_manager::UserID& user_id,
                                            const std::string& wrapped_secret,
                                            const std::string& raw_session_key) {
   if (state_ != STATE_RUNNING || user_id != user_id_)
     return;
 
   if (!GetScreenlockBridgeInstance()->IsLocked())
     return;
 
   if (type_ != TYPE_SIGNIN) {
     Cancel(user_id_);
@@ skipping 11 matching lines @@
 #if defined(OS_CHROMEOS)
   key_label = chromeos::EasyUnlockKeyManager::GetKeyLabel(0u);
 #endif  // defined(OS_CHROMEOS)
 
   const bool kSuccess = true;
   finalized_callback_.Run(type_, kSuccess, user_id, unwrapped_secret,
                           key_label);
   state_ = STATE_DONE;
 }
 
-void EasyUnlockAuthAttempt::Cancel(const std::string& user_id) {
+void EasyUnlockAuthAttempt::Cancel(const user_manager::UserID& user_id) {
   state_ = STATE_DONE;
 
   const bool kFailure = false;
   finalized_callback_.Run(type_, kFailure, user_id, std::string(),
                           std::string());
 }