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

chrome/browser/signin/easy_unlock_app_manager.h

Index: chrome/browser/signin/easy_unlock_app_manager.h
diff --git a/chrome/browser/signin/easy_unlock_app_manager.h b/chrome/browser/signin/easy_unlock_app_manager.h
index 1b7ac8b0f0d7116d47c1731abddef5b86307f0fc..08def67fcea9373f86ab16aed8ebcdb0d3902fef 100644
--- a/chrome/browser/signin/easy_unlock_app_manager.h
+++ b/chrome/browser/signin/easy_unlock_app_manager.h
@@ -15,6 +15,10 @@ namespace extensions {
 class ExtensionSystem;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 // Used to manage Easy Unlock app's lifetime and to dispatch events to the app.
 // It's main purpose is to abstract extension system from the rest of easy
 // unlock code.
@@ -46,7 +50,7 @@ class EasyUnlockAppManager {
   virtual void ReloadApp() = 0;
 
   // Sends easyUnlockPrivate.onUserInfoUpdate event to Easy Unlock app.
-  virtual bool SendUserUpdatedEvent(const std::string& user_id,
+  virtual bool SendUserUpdatedEvent(const user_manager::UserID& user_id,
                                     bool is_logged_in,
                                     bool data_ready) = 0;