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

chrome/browser/chromeos/login/supervised/supervised_user_authenticator.cc

Index: chrome/browser/chromeos/login/supervised/supervised_user_authenticator.cc
diff --git a/chrome/browser/chromeos/login/supervised/supervised_user_authenticator.cc b/chrome/browser/chromeos/login/supervised/supervised_user_authenticator.cc
index a0f9eab12e33d41df22317281adbc87270dc3f8a..d9dabd52a6fa846d1678d6d23ad526a718a01102 100644
--- a/chrome/browser/chromeos/login/supervised/supervised_user_authenticator.cc
+++ b/chrome/browser/chromeos/login/supervised/supervised_user_authenticator.cc
@@ -68,7 +68,7 @@ void Mount(SupervisedUserAuthenticator::AuthAttempt* attempt,
   Key key(attempt->password);
   key.Transform(Key::KEY_TYPE_SALTED_SHA256_TOP_HALF, system_salt);
   cryptohome::AsyncMethodCaller::GetInstance()->AsyncMount(
-      attempt->username,
+      attempt->user_id,
       key.GetSecret(),
       flags,
       base::Bind(&TriggerResolveWithLoginTimeMarker,
@@ -77,7 +77,7 @@ void Mount(SupervisedUserAuthenticator::AuthAttempt* attempt,
                  resolver));
 
   cryptohome::AsyncMethodCaller::GetInstance()->AsyncGetSanitizedUsername(
-      attempt->username,
+      attempt->user_id,
       base::Bind(&TriggerResolveResult, attempt, resolver));
 }
 
@@ -95,7 +95,7 @@ void AddKey(SupervisedUserAuthenticator::AuthAttempt* attempt,
   Key master_key(plain_text_master_key);
   master_key.Transform(Key::KEY_TYPE_SALTED_SHA256_TOP_HALF, system_salt);
   cryptohome::AsyncMethodCaller::GetInstance()->AsyncAddKey(
-      attempt->username,
+      attempt->user_id,
       user_key.GetSecret(),
       master_key.GetSecret(),
       base::Bind(&TriggerResolveWithLoginTimeMarker,
@@ -111,12 +111,10 @@ SupervisedUserAuthenticator::SupervisedUserAuthenticator(
     : consumer_(consumer) {}
 
 void SupervisedUserAuthenticator::AuthenticateToMount(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const std::string& password) {
-  std::string canonicalized = gaia::CanonicalizeEmail(username);
-
   current_state_.reset(new SupervisedUserAuthenticator::AuthAttempt(
-      canonicalized, password, false));
+      user_id, password, false));
 
   SystemSaltGetter::Get()->GetSystemSalt(
       base::Bind(&Mount,
@@ -126,12 +124,10 @@ void SupervisedUserAuthenticator::AuthenticateToMount(
 }
 
 void SupervisedUserAuthenticator::AuthenticateToCreate(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const std::string& password) {
-  std::string canonicalized = gaia::CanonicalizeEmail(username);
-
   current_state_.reset(new SupervisedUserAuthenticator::AuthAttempt(
-      canonicalized, password, false));
+      user_id, password, false));
 
   SystemSaltGetter::Get()->GetSystemSalt(
       base::Bind(&Mount,
@@ -141,13 +137,11 @@ void SupervisedUserAuthenticator::AuthenticateToCreate(
 }
 
 void SupervisedUserAuthenticator::AddMasterKey(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const std::string& password,
     const std::string& master_key) {
-  std::string canonicalized = gaia::CanonicalizeEmail(username);
-
   current_state_.reset(new SupervisedUserAuthenticator::AuthAttempt(
-      canonicalized, password, true));
+      user_id, password, true));
 
   SystemSaltGetter::Get()->GetSystemSalt(
       base::Bind(&AddKey,
@@ -288,10 +282,10 @@ SupervisedUserAuthenticator::AuthState
 }
 
 SupervisedUserAuthenticator::AuthAttempt::AuthAttempt(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const std::string& password,
     bool add_key_attempt)
-    : username(username),
+    : user_id(user_id),
       password(password),
       add_key(add_key_attempt),
       cryptohome_complete_(false),