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

chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.cc
index 18c0ac30d71253997b2b4a0b93dcbc8711f41c2f..f9e56ef1c126c0dc2d6abc1e3706bc82d34211b1 100644
--- a/chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.cc
@@ -6,6 +6,7 @@
 
 #include "chrome/browser/chromeos/login/ui/models/user_board_model.h"
 #include "components/login/localized_values_builder.h"
+#include "components/user_manager/user_id.h"
 
 namespace chromeos {
 
@@ -37,37 +38,37 @@ void UserBoardScreenHandler::HandleGetUsers() {
   model_->SendUserList();
 }
 
-void UserBoardScreenHandler::HandleHardlockPod(const std::string& user_id) {
+void UserBoardScreenHandler::HandleHardlockPod(const std::string& user_email) {
   CHECK(model_);
-  model_->HardLockPod(user_id);
+  model_->HardLockPod(user_manager::UserID::FromUserEmail(user_email));
 }
 
-void UserBoardScreenHandler::HandleAttemptUnlock(const std::string& user_id) {
+void UserBoardScreenHandler::HandleAttemptUnlock(const std::string& user_email) {
   CHECK(model_);
-  model_->AttemptEasyUnlock(user_id);
+  model_->AttemptEasyUnlock(user_manager::UserID::FromUserEmail(user_email));
 }
 
 void UserBoardScreenHandler::HandleRecordClickOnLockIcon(
-    const std::string& user_id) {
+    const std::string& user_email) {
   CHECK(model_);
-  model_->RecordClickOnLockIcon(user_id);
+  model_->RecordClickOnLockIcon(user_manager::UserID::FromUserEmail(user_email));
 }
 
 //----------------- API
 
 void UserBoardScreenHandler::SetPublicSessionDisplayName(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     const std::string& display_name) {
-  CallJS("login.AccountPickerScreen.setPublicSessionDisplayName", user_id,
+  CallJS("login.AccountPickerScreen.setPublicSessionDisplayName", user_id.GetUserEmail(),
          display_name);
 }
 
 void UserBoardScreenHandler::SetPublicSessionLocales(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     scoped_ptr<base::ListValue> locales,
     const std::string& default_locale,
     bool multiple_recommended_locales) {
-  CallJS("login.AccountPickerScreen.setPublicSessionLocales", user_id, *locales,
+  CallJS("login.AccountPickerScreen.setPublicSessionLocales", user_id.GetUserEmail(), *locales,
          default_locale, multiple_recommended_locales);
 }
 
@@ -76,20 +77,20 @@ void UserBoardScreenHandler::ShowBannerMessage(const base::string16& message) {
 }
 
 void UserBoardScreenHandler::ShowUserPodCustomIcon(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     const base::DictionaryValue& icon) {
-  CallJS("login.AccountPickerScreen.showUserPodCustomIcon", user_id, icon);
+  CallJS("login.AccountPickerScreen.showUserPodCustomIcon", user_id.GetUserEmail(), icon);
 }
 
-void UserBoardScreenHandler::HideUserPodCustomIcon(const std::string& user_id) {
-  CallJS("login.AccountPickerScreen.hideUserPodCustomIcon", user_id);
+void UserBoardScreenHandler::HideUserPodCustomIcon(const user_manager::UserID& user_id) {
+  CallJS("login.AccountPickerScreen.hideUserPodCustomIcon", user_id.GetUserEmail());
 }
 
 void UserBoardScreenHandler::SetAuthType(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     proximity_auth::ScreenlockBridge::LockHandler::AuthType auth_type,
     const base::string16& initial_value) {
-  CallJS("login.AccountPickerScreen.setAuthType", user_id,
+  CallJS("login.AccountPickerScreen.setAuthType", user_id.GetUserEmail(),
          static_cast<int>(auth_type), base::StringValue(initial_value));
 }