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

chromeos/cryptohome/cryptohome_parameters.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 "chromeos/cryptohome/cryptohome_parameters.h"
 
 #include "chromeos/dbus/cryptohome/key.pb.h"
 
 namespace cryptohome {
 
-Identification::Identification(const std::string& user_id) : user_id(user_id) {
+Identification::Identification(const user_manager::UserID& user_id) : user_id(user_id) {
 }
 
 bool Identification::operator==(const Identification& other) const {
   return user_id == other.user_id;
 }
 
 KeyDefinition::AuthorizationData::Secret::Secret() : encrypt(false),
                                                      sign(false),
                                                      wrapped(false) {
 }
@@ skipping 153 matching lines @@
 }
 
 bool MountParameters::operator==(const MountParameters& other) const {
   return ephemeral == other.ephemeral && create_keys == other.create_keys;
 }
 
 MountParameters::~MountParameters() {
 }
 
 }  // namespace cryptohome