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

chrome/browser/signin/easy_unlock_service_regular.cc

Index: chrome/browser/signin/easy_unlock_service_regular.cc
diff --git a/chrome/browser/signin/easy_unlock_service_regular.cc b/chrome/browser/signin/easy_unlock_service_regular.cc
index b02d769c63fb10c99a77e4721da353a8eb14942d..8e7ab3652e13b29a081f095c15ac26a9e9e9ec71 100644
--- a/chrome/browser/signin/easy_unlock_service_regular.cc
+++ b/chrome/browser/signin/easy_unlock_service_regular.cc
@@ -93,14 +93,8 @@ EasyUnlockService::Type EasyUnlockServiceRegular::GetType() const {
   return EasyUnlockService::TYPE_REGULAR;
 }
 
-std::string EasyUnlockServiceRegular::GetUserEmail() const {
-  const SigninManagerBase* signin_manager =
-      SigninManagerFactory::GetForProfileIfExists(profile());
-  // |profile| has to be a signed-in profile with SigninManager already
-  // created. Otherwise, just crash to collect stack.
-  DCHECK(signin_manager);
-  const std::string user_email = signin_manager->GetAuthenticatedUsername();
-  return user_email.empty() ? user_email : gaia::CanonicalizeEmail(user_email);
+user_manager::UserID EasyUnlockServiceRegular::GetUserID() const {
+  return user_manager::UserID::FromUserEmail(GetUserEmail());
 }
 
 void EasyUnlockServiceRegular::LaunchSetup() {
@@ -151,7 +145,7 @@ void EasyUnlockServiceRegular::SetHardlockAfterKeyOperation(
     EasyUnlockScreenlockStateHandler::HardlockState state_on_success,
     bool success) {
   if (success)
-    SetHardlockStateForUser(GetUserEmail(), state_on_success);
+    SetHardlockStateForUser(GetUserID(), state_on_success);
 
   // Even if the refresh keys operation suceeded, we still fetch and check the
   // cryptohome keys against the keys in local preferences as a sanity check.
@@ -267,13 +261,13 @@ std::string EasyUnlockServiceRegular::GetWrappedSecret() const {
 }
 
 void EasyUnlockServiceRegular::RecordEasySignInOutcome(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     bool success) const {
   NOTREACHED();
 }
 
 void EasyUnlockServiceRegular::RecordPasswordLoginEvent(
-    const std::string& user_id) const {
+    const user_manager::UserID& user_id) const {
   NOTREACHED();
 }
 
@@ -392,10 +386,20 @@ void EasyUnlockServiceRegular::OnScreenDidUnlock(
 }
 
 void EasyUnlockServiceRegular::OnFocusedUserChanged(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   // Nothing to do.
 }
 
+std::string EasyUnlockServiceRegular::GetUserEmail() const {
+  const SigninManagerBase* signin_manager =
+      SigninManagerFactory::GetForProfileIfExists(profile());
+  // |profile| has to be a signed-in profile with SigninManager already
+  // created. Otherwise, just crash to collect stack.
+  DCHECK(signin_manager);
+  const std::string user_email = signin_manager->GetAuthenticatedUsername();
+  return user_email.empty() ? user_email : gaia::CanonicalizeEmail(user_email);
+}
+
 void EasyUnlockServiceRegular::OnPrefsChanged() {
   SyncProfilePrefsToLocalState();
   UpdateAppState();