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

chrome/browser/signin/easy_unlock_auth_attempt.h

Index: chrome/browser/signin/easy_unlock_auth_attempt.h
diff --git a/chrome/browser/signin/easy_unlock_auth_attempt.h b/chrome/browser/signin/easy_unlock_auth_attempt.h
index 18bc9afa722751a9a6a7eee5c1b1dddb1d11e281..d236bb90b0902907eb6bb42bafd8ce8ed0e8701b 100644
--- a/chrome/browser/signin/easy_unlock_auth_attempt.h
+++ b/chrome/browser/signin/easy_unlock_auth_attempt.h
@@ -9,6 +9,7 @@
 
 #include "base/callback.h"
 #include "base/macros.h"
+#include "components/user_manager/user_id.h"
 
 class EasyUnlockAppManager;
 
@@ -33,13 +34,13 @@ class EasyUnlockAuthAttempt {
   // and |key_label| is the label of the corresponding cryptohome key.
   typedef base::Callback<void(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)>
       FinalizedCallback;
 
   EasyUnlockAuthAttempt(EasyUnlockAppManager* app_manager,
-                        const std::string& user_id,
+                        const user_manager::UserID& user_id,
                         Type type,
                         const FinalizedCallback& finalized_callback);
   ~EasyUnlockAuthAttempt();
@@ -51,14 +52,14 @@ class EasyUnlockAuthAttempt {
   // Finalizes an unlock attempt. It unlocks the screen if |success| is true.
   // If |this| has TYPE_SIGNIN type, calling this method will cause signin
   // failure equivalent to cancelling the attempt.
-  void FinalizeUnlock(const std::string& user_id, bool success);
+  void FinalizeUnlock(const user_manager::UserID& user_id, bool success);
 
   // Finalizes signin attempt. It tries to log in using the secret derived from
   // |wrapped_secret| decrypted by |session_key|. If the decryption fails, it
   // fails the signin attempt.
   // If called on an object with TYPE_UNLOCK type, it will cause unlock failure
   // equivalent to cancelling the request.
-  void FinalizeSignin(const std::string& user_id,
+  void FinalizeSignin(const user_manager::UserID& user_id,
                       const std::string& wrapped_secret,
                       const std::string& session_key);
 
@@ -71,11 +72,11 @@ class EasyUnlockAuthAttempt {
   };
 
   // Cancels the attempt.
-  void Cancel(const std::string& user_id);
+  void Cancel(const user_manager::UserID& user_id);
 
   EasyUnlockAppManager* app_manager_;
   State state_;
-  std::string user_id_;
+  user_manager::UserID user_id_;
   Type type_;
 
   FinalizedCallback finalized_callback_;