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

chrome/browser/chromeos/policy/policy_cert_service_factory.cc

Index: chrome/browser/chromeos/policy/policy_cert_service_factory.cc
diff --git a/chrome/browser/chromeos/policy/policy_cert_service_factory.cc b/chrome/browser/chromeos/policy/policy_cert_service_factory.cc
index 52a69f3a6da7e68aa98d9847bd83a6098103d99e..186df23b1ed13b41dc9c58ab20807edea98abddd 100644
--- a/chrome/browser/chromeos/policy/policy_cert_service_factory.cc
+++ b/chrome/browser/chromeos/policy/policy_cert_service_factory.cc
@@ -47,26 +47,26 @@ PolicyCertServiceFactory* PolicyCertServiceFactory::GetInstance() {
 
 // static
 void PolicyCertServiceFactory::SetUsedPolicyCertificates(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   if (UsedPolicyCertificates(user_id))
     return;
   ListPrefUpdate update(g_browser_process->local_state(),
                         prefs::kUsedPolicyCertificates);
-  update->AppendString(user_id);
+  update->AppendString(user_id.GetUserEmail());
 }
 
 // static
 void PolicyCertServiceFactory::ClearUsedPolicyCertificates(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   ListPrefUpdate update(g_browser_process->local_state(),
                         prefs::kUsedPolicyCertificates);
-  update->Remove(base::StringValue(user_id), NULL);
+  update->Remove(base::StringValue(user_id.GetUserEmail()), NULL);
 }
 
 // static
 bool PolicyCertServiceFactory::UsedPolicyCertificates(
-    const std::string& user_id) {
-  base::StringValue value(user_id);
+    const user_manager::UserID& user_id) {
+  base::StringValue value(user_id.GetUserEmail());
   const base::ListValue* list =
       g_browser_process->local_state()->GetList(prefs::kUsedPolicyCertificates);
   if (!list) {
@@ -108,7 +108,7 @@ KeyedService* PolicyCertServiceFactory::BuildServiceInstanceFor(
   // TODO(joaodasilva): remove this, eventually.
   PrefService* prefs = profile->GetOriginalProfile()->GetPrefs();
   if (prefs->GetBoolean(prefs::kUsedPolicyCertificatesOnce)) {
-    SetUsedPolicyCertificates(user->email());
+    SetUsedPolicyCertificates(user->GetUserID());
     prefs->ClearPref(prefs::kUsedPolicyCertificatesOnce);
 
     if (user_manager->GetLoggedInUsers().size() > 1u) {
@@ -128,7 +128,7 @@ KeyedService* PolicyCertServiceFactory::BuildServiceInstanceFor(
   if (!net_conf_updater)
     return NULL;
 
-  return new PolicyCertService(user->email(), net_conf_updater, user_manager);
+  return new PolicyCertService(user->GetUserID(), net_conf_updater, user_manager);
 }
 
 content::BrowserContext* PolicyCertServiceFactory::GetBrowserContextToUse(