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

chrome/browser/chromeos/login/reauth_stats.cc

Index: chrome/browser/chromeos/login/reauth_stats.cc
diff --git a/chrome/browser/chromeos/login/reauth_stats.cc b/chrome/browser/chromeos/login/reauth_stats.cc
index f442c974f012efa6401590731e93e96e03bdffe0..c2bdbe3d64952b15e2afbc00e11aece69b2be1ca 100644
--- a/chrome/browser/chromeos/login/reauth_stats.cc
+++ b/chrome/browser/chromeos/login/reauth_stats.cc
@@ -9,7 +9,7 @@
 
 namespace chromeos {
 
-void RecordReauthReason(const std::string& user_id, ReauthReason reason) {
+void RecordReauthReason(const user_manager::UserID& user_id, ReauthReason reason) {
   user_manager::UserManager* user_manager = user_manager::UserManager::Get();
   int old_reason;
   // We record only the first value, skipping everything else, except "none"
@@ -21,7 +21,7 @@ void RecordReauthReason(const std::string& user_id, ReauthReason reason) {
   }
 }
 
-void SendReauthReason(const std::string& user_id) {
+void SendReauthReason(const user_manager::UserID& user_id) {
   user_manager::UserManager* user_manager = user_manager::UserManager::Get();
   int reauth_reason;
   if (user_manager->FindReauthReason(user_id, &reauth_reason) &&