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

chrome/browser/signin/easy_unlock_service_signin_chromeos.cc

Index: chrome/browser/signin/easy_unlock_service_signin_chromeos.cc
diff --git a/chrome/browser/signin/easy_unlock_service_signin_chromeos.cc b/chrome/browser/signin/easy_unlock_service_signin_chromeos.cc
index ad3536f856e0c06e985c3d3a5f3ae6af37c9bdf6..2ee6cb89f874739ef32574395adb06e64b6e7c6b 100644
--- a/chrome/browser/signin/easy_unlock_service_signin_chromeos.cc
+++ b/chrome/browser/signin/easy_unlock_service_signin_chromeos.cc
@@ -38,7 +38,7 @@ uint32 GetNextBackoffInterval(uint32 backoff) {
 }
 
 void LoadDataForUser(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     uint32 backoff_ms,
     const chromeos::EasyUnlockKeyManager::GetDeviceDataListCallback& callback);
 
@@ -49,7 +49,7 @@ void LoadDataForUser(
 // |LoadDataForUser| call with some backoff. If no further retires are allowed,
 // it invokes |callback| with the |LoadDataForUser| results.
 void RetryDataLoadOnError(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     uint32 backoff_ms,
     const chromeos::EasyUnlockKeyManager::GetDeviceDataListCallback& callback,
     bool success,
@@ -73,7 +73,7 @@ void RetryDataLoadOnError(
 
 // Loads device data list associated with the user's Easy unlock keys.
 void LoadDataForUser(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     uint32 backoff_ms,
     const chromeos::EasyUnlockKeyManager::GetDeviceDataListCallback& callback) {
   chromeos::EasyUnlockKeyManager* key_manager =
@@ -95,6 +95,7 @@ EasyUnlockServiceSignin::UserData::~UserData() {}
 
 EasyUnlockServiceSignin::EasyUnlockServiceSignin(Profile* profile)
     : EasyUnlockService(profile),
+      user_id_(std::string(), std::string()),
       allow_cryptohome_backoff_(true),
       service_active_(false),
       user_pod_last_focused_timestamp_(base::TimeTicks::Now()),
@@ -104,7 +105,7 @@ EasyUnlockServiceSignin::EasyUnlockServiceSignin(Profile* profile)
 EasyUnlockServiceSignin::~EasyUnlockServiceSignin() {
 }
 
-void EasyUnlockServiceSignin::SetCurrentUser(const std::string& user_id) {
+void EasyUnlockServiceSignin::SetCurrentUser(const user_manager::UserID& user_id) {
   OnFocusedUserChanged(user_id);
 }
 
@@ -112,7 +113,7 @@ EasyUnlockService::Type EasyUnlockServiceSignin::GetType() const {
   return EasyUnlockService::TYPE_SIGNIN;
 }
 
-std::string EasyUnlockServiceSignin::GetUserEmail() const {
+user_manager::UserID EasyUnlockServiceSignin::GetUserID() const {
   return user_id_;
 }
 
@@ -177,9 +178,9 @@ std::string EasyUnlockServiceSignin::GetWrappedSecret() const {
 }
 
 void EasyUnlockServiceSignin::RecordEasySignInOutcome(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     bool success) const {
-  DCHECK_EQ(GetUserEmail(), user_id);
+  DCHECK(GetUserID() == user_id);
 
   RecordEasyUnlockSigninEvent(
       success ? EASY_UNLOCK_SUCCESS : EASY_UNLOCK_FAILURE);
@@ -191,10 +192,10 @@ void EasyUnlockServiceSignin::RecordEasySignInOutcome(
 }
 
 void EasyUnlockServiceSignin::RecordPasswordLoginEvent(
-    const std::string& user_id) const {
+    const user_manager::UserID& user_id) const {
   // This happens during tests, where a user could log in without the user pod
   // being focused.
-  if (GetUserEmail() != user_id)
+  if (GetUserID() != user_id)
     return;
 
   if (!IsEnabled())
@@ -284,7 +285,7 @@ void EasyUnlockServiceSignin::OnScreenDidUnlock(
   Shutdown();
 }
 
-void EasyUnlockServiceSignin::OnFocusedUserChanged(const std::string& user_id) {
+void EasyUnlockServiceSignin::OnFocusedUserChanged(const user_manager::UserID& user_id) {
   if (user_id_ == user_id)
     return;
 
@@ -330,7 +331,7 @@ void EasyUnlockServiceSignin::LoadCurrentUserDataIfNeeded() {
   if (user_id_.empty() || !service_active_)
     return;
 
-  std::map<std::string, UserData*>::iterator it = user_data_.find(user_id_);
+  std::map<user_manager::UserID, UserData*>::iterator it = user_data_.find(user_id_);
   if (it == user_data_.end())
     user_data_.insert(std::make_pair(user_id_, new UserData()));
 
@@ -349,7 +350,7 @@ void EasyUnlockServiceSignin::LoadCurrentUserDataIfNeeded() {
 }
 
 void EasyUnlockServiceSignin::OnUserDataLoaded(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     bool success,
     const chromeos::EasyUnlockDeviceKeyDataList& devices) {
   allow_cryptohome_backoff_ = false;
@@ -385,7 +386,7 @@ const EasyUnlockServiceSignin::UserData*
   if (user_id_.empty())
     return NULL;
 
-  std::map<std::string, UserData*>::const_iterator it =
+  std::map<user_manager::UserID, UserData*>::const_iterator it =
       user_data_.find(user_id_);
   if (it == user_data_.end())
     return NULL;