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

chrome/browser/chromeos/login/easy_unlock/easy_unlock_user_login_flow.h

Index: chrome/browser/chromeos/login/easy_unlock/easy_unlock_user_login_flow.h
diff --git a/chrome/browser/chromeos/login/easy_unlock/easy_unlock_user_login_flow.h b/chrome/browser/chromeos/login/easy_unlock/easy_unlock_user_login_flow.h
index 0f069bb57055b0569291193a3c9f8e054aa7974a..af3bdf259b2aee91e2925942d0e29da01ea8c9a7 100644
--- a/chrome/browser/chromeos/login/easy_unlock/easy_unlock_user_login_flow.h
+++ b/chrome/browser/chromeos/login/easy_unlock/easy_unlock_user_login_flow.h
@@ -10,12 +10,16 @@
 #include "base/macros.h"
 #include "chrome/browser/chromeos/login/user_flow.h"
 
+namespace user_manager {
+class UserID;
+}
+
 // Handler for login flow initiazted by Easy Signin login attempt.
 // The only difference to the default login flow is hanlding of the auth
 // failure.
 class EasyUnlockUserLoginFlow : public chromeos::ExtendedUserFlow {
  public:
-  explicit EasyUnlockUserLoginFlow(const std::string& user_id);
+  explicit EasyUnlockUserLoginFlow(const user_manager::UserID& user_id);
   ~EasyUnlockUserLoginFlow() override;
 
  private: