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

chrome/browser/chromeos/policy/device_local_account_policy_provider.cc

Index: chrome/browser/chromeos/policy/device_local_account_policy_provider.cc
diff --git a/chrome/browser/chromeos/policy/device_local_account_policy_provider.cc b/chrome/browser/chromeos/policy/device_local_account_policy_provider.cc
index ca40ec6395be301d49a17859bd5a98cda41f179d..30308e4512ab22d367d6f1858d8f7c814103c438 100644
--- a/chrome/browser/chromeos/policy/device_local_account_policy_provider.cc
+++ b/chrome/browser/chromeos/policy/device_local_account_policy_provider.cc
@@ -20,7 +20,7 @@
 namespace policy {
 
 DeviceLocalAccountPolicyProvider::DeviceLocalAccountPolicyProvider(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     DeviceLocalAccountPolicyService* service,
     scoped_ptr<PolicyMap> chrome_policy_overrides)
     : user_id_(user_id),
@@ -40,7 +40,7 @@ DeviceLocalAccountPolicyProvider::~DeviceLocalAccountPolicyProvider() {
 // static
 scoped_ptr<DeviceLocalAccountPolicyProvider>
 DeviceLocalAccountPolicyProvider::Create(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     DeviceLocalAccountPolicyService* device_local_account_policy_service) {
   DeviceLocalAccount::Type type;
   if (!device_local_account_policy_service ||
@@ -119,7 +119,7 @@ void DeviceLocalAccountPolicyProvider::RefreshPolicies() {
 }
 
 void DeviceLocalAccountPolicyProvider::OnPolicyUpdated(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   if (user_id == user_id_)
     UpdateFromBroker();
 }