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

chrome/browser/chromeos/policy/device_local_account_external_data_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/device_local_account_external_data_service.h"
 
 #include <set>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 29 matching lines @@
   for (ExternalDataManagerMap::const_iterator it =
            external_data_managers_.begin();
        it != external_data_managers_.end(); ++it) {
     DCHECK(it->second->HasOneRef());
   }
 #endif  // !defined(NDEBUG)
   backend_task_runner_->DeleteSoon(FROM_HERE, resource_cache_.release());
 }
 
 void DeviceLocalAccountExternalDataService::OnPolicyUpdated(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
 }
 
 void DeviceLocalAccountExternalDataService::OnDeviceLocalAccountsChanged() {
   std::set<std::string> account_ids;
   for (ExternalDataManagerMap::iterator it = external_data_managers_.begin();
        it != external_data_managers_.end(); ) {
     if (it->second->HasOneRef()) {
       external_data_managers_.erase(it++);
     } else {
       account_ids.insert(it->first);
@@ skipping 18 matching lines @@
         base::Bind(&GetChromePolicyDetails),
         backend_task_runner_,
         io_task_runner_,
         resource_cache_.get());
   }
   external_data_manager->SetPolicyStore(policy_store);
   return external_data_manager;
 }
 
 }  // namespace policy