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

chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.cc

Index: chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.cc
diff --git a/chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.cc b/chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.cc
index 6338752ac32a1240e4ca9cd19e3c7ccfc3489fe9..5463b38edb403bec8273eaafdf89bec8cccf32d4 100644
--- a/chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.cc
+++ b/chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.cc
@@ -68,7 +68,7 @@ void BootstrapUserContextInitializer::StartTokenFetch(
 }
 
 void BootstrapUserContextInitializer::StartCheckExistingKeys() {
-  const std::string& user_id = user_context_.GetUserID();
+  const user_manager::UserID& user_id = user_context_.GetUserID();
 
   // Use random key for the first time user.
   if (!user_manager::UserManager::Get()->IsKnownUser(user_id)) {
@@ -106,7 +106,7 @@ void BootstrapUserContextInitializer::OnGetEasyUnlockData(
 void BootstrapUserContextInitializer::OnEasyUnlockAuthenticated(
     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) {
   DCHECK_EQ(EasyUnlockAuthAttempt::TYPE_SIGNIN, auth_attempt_type);
@@ -176,8 +176,9 @@ void BootstrapUserContextInitializer::OnGetUserInfoResponse(
     return;
   }
 
-  user_context_.SetUserID(email);
-  user_context_.SetGaiaID(gaia_id);
+  const user_manager::UserID user_id(gaia_id, email);
+
+  user_context_.SetUserID(user_id);
   StartCheckExistingKeys();
 }