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

chrome/browser/signin/easy_unlock_auth_attempt.cc

Index: chrome/browser/signin/easy_unlock_auth_attempt.cc
diff --git a/chrome/browser/signin/easy_unlock_auth_attempt.cc b/chrome/browser/signin/easy_unlock_auth_attempt.cc
index 5560754a974d7de04eb39e040fec1a8452dc99e2..cf80df15581147666d5865033be33bccdf0e15b2 100644
--- a/chrome/browser/signin/easy_unlock_auth_attempt.cc
+++ b/chrome/browser/signin/easy_unlock_auth_attempt.cc
@@ -48,7 +48,7 @@ std::string UnwrapSecret(const std::string& wrapped_secret,
 void DefaultAuthAttemptFinalizedHandler(
     EasyUnlockAuthAttempt::Type auth_attempt_type,
     bool success,
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     const std::string& key_secret,
     const std::string& key_label) {
   if (!GetScreenlockBridgeInstance()->IsLocked())
@@ -80,7 +80,7 @@ void DefaultAuthAttemptFinalizedHandler(
 
 EasyUnlockAuthAttempt::EasyUnlockAuthAttempt(
     EasyUnlockAppManager* app_manager,
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     Type type,
     const FinalizedCallback& finalized_callback)
     : app_manager_(app_manager),
@@ -121,7 +121,7 @@ bool EasyUnlockAuthAttempt::Start() {
   return true;
 }
 
-void EasyUnlockAuthAttempt::FinalizeUnlock(const std::string& user_id,
+void EasyUnlockAuthAttempt::FinalizeUnlock(const user_manager::UserID& user_id,
                                            bool success) {
   if (state_ != STATE_RUNNING || user_id != user_id_)
     return;
@@ -139,7 +139,7 @@ void EasyUnlockAuthAttempt::FinalizeUnlock(const std::string& user_id,
   state_ = STATE_DONE;
 }
 
-void EasyUnlockAuthAttempt::FinalizeSignin(const std::string& user_id,
+void EasyUnlockAuthAttempt::FinalizeSignin(const user_manager::UserID& user_id,
                                            const std::string& wrapped_secret,
                                            const std::string& raw_session_key) {
   if (state_ != STATE_RUNNING || user_id != user_id_)
@@ -171,7 +171,7 @@ void EasyUnlockAuthAttempt::FinalizeSignin(const std::string& user_id,
   state_ = STATE_DONE;
 }
 
-void EasyUnlockAuthAttempt::Cancel(const std::string& user_id) {
+void EasyUnlockAuthAttempt::Cancel(const user_manager::UserID& user_id) {
   state_ = STATE_DONE;
 
   const bool kFailure = false;