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

chrome/browser/chromeos/policy/policy_cert_service.cc

 // Copyright 2013 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/policy/policy_cert_service.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "chrome/browser/chromeos/policy/policy_cert_service_factory.h"
 #include "chrome/browser/chromeos/policy/policy_cert_verifier.h"
 #include "components/user_manager/user_manager.h"
 #include "content/public/browser/browser_thread.h"
 #include "net/cert/x509_certificate.h"
 
 namespace policy {
 
 PolicyCertService::~PolicyCertService() {
   DCHECK(cert_verifier_)
       << "CreatePolicyCertVerifier() must be called after construction.";
 }
 
 PolicyCertService::PolicyCertService(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     UserNetworkConfigurationUpdater* net_conf_updater,
     user_manager::UserManager* user_manager)
     : cert_verifier_(NULL),
       user_id_(user_id),
       net_conf_updater_(net_conf_updater),
       user_manager_(user_manager),
       has_trust_anchors_(false),
       weak_ptr_factory_(this) {
   DCHECK(net_conf_updater_);
   DCHECK(user_manager_);
 }
 
-PolicyCertService::PolicyCertService(const std::string& user_id,
+PolicyCertService::PolicyCertService(const user_manager::UserID& user_id,
                                      PolicyCertVerifier* verifier,
                                      user_manager::UserManager* user_manager)
     : cert_verifier_(verifier),
       user_id_(user_id),
       net_conf_updater_(NULL),
       user_manager_(user_manager),
       has_trust_anchors_(false),
       weak_ptr_factory_(this) {
 }
 
@@ skipping 53 matching lines @@
 void PolicyCertService::Shutdown() {
   weak_ptr_factory_.InvalidateWeakPtrs();
   if (net_conf_updater_)
     net_conf_updater_->RemoveTrustedCertsObserver(this);
   OnTrustAnchorsChanged(net::CertificateList());
   net_conf_updater_ = NULL;
 }
 
 // static
 scoped_ptr<PolicyCertService> PolicyCertService::CreateForTesting(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     PolicyCertVerifier* verifier,
     user_manager::UserManager* user_manager) {
   return make_scoped_ptr(
       new PolicyCertService(user_id, verifier, user_manager));
 }
 
 }  // namespace policy