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

chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.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/chromeos/login/easy_unlock/bootstrap_user_context_initializer.h"
 
 #include <vector>
 
 #include "base/strings/string_util.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 50 matching lines @@
   client_info.client_id = gaia_urls->oauth2_chrome_client_id();
   client_info.client_secret = gaia_urls->oauth2_chrome_client_secret();
 
   token_fetcher_.reset(
       new gaia::GaiaOAuthClient(g_browser_process->system_request_context()));
   token_fetcher_->GetTokensFromAuthCode(client_info, auth_code, kMaxGaiaRetries,
                                         this);
 }
 
 void BootstrapUserContextInitializer::StartCheckExistingKeys() {
-  const std::string& user_id = user_context_.GetUserID();
+  const user_manager::UserID& user_id = user_context_.GetUserID();
 
   // Use random key for the first time user.
   if (!user_manager::UserManager::Get()->IsKnownUser(user_id)) {
     CreateRandomKey();
     return;
   }
 
   EasyUnlockKeyManager* key_manager =
       UserSessionManager::GetInstance()->GetEasyUnlockKeyManager();
   key_manager->GetDeviceDataList(
@@ skipping 17 matching lines @@
   service->AddObserver(this);
 
   static_cast<EasyUnlockServiceSignin*>(service)
       ->SetCurrentUser(user_context_.GetUserID());
   OnScreenlockStateChanged(service->GetScreenlockState());
 }
 
 void BootstrapUserContextInitializer::OnEasyUnlockAuthenticated(
     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) {
   DCHECK_EQ(EasyUnlockAuthAttempt::TYPE_SIGNIN, auth_attempt_type);
   if (!success || key_secret.empty()) {
     LOG(ERROR) << "Failed to sign-in using existing Smart lock key.";
     Notify(false);
     return;
   }
 
   user_context_.SetKey(Key(key_secret));
@@ skipping 49 matching lines @@
     scoped_ptr<base::DictionaryValue> user_info) {
   std::string email;
   std::string gaia_id;
   if (!user_info->GetString("email", &email) ||
       !user_info->GetString("id", &gaia_id)) {
     LOG(ERROR) << "Bad user info.";
     Notify(false);
     return;
   }
 
-  user_context_.SetUserID(email);
-  user_context_.SetGaiaID(gaia_id);
+  const user_manager::UserID user_id(gaia_id, email);
+
+  user_context_.SetUserID(user_id);
   StartCheckExistingKeys();
 }
 
 void BootstrapUserContextInitializer::OnOAuthError() {
   LOG(ERROR) << "Auth error.";
   Notify(false);
 }
 
 void BootstrapUserContextInitializer::OnNetworkError(int response_code) {
   LOG(ERROR) << "Network error.";
@@ skipping 11 matching lines @@
       EasyUnlockService::Get(ProfileHelper::GetSigninProfile());
   service->RemoveObserver(this);
 
   service->AttemptAuth(
       user_context_.GetUserID(),
       base::Bind(&BootstrapUserContextInitializer::OnEasyUnlockAuthenticated,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
 }  // namespace chromeos