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

components/proximity_auth/screenlock_bridge.h

Index: components/proximity_auth/screenlock_bridge.h
diff --git a/components/proximity_auth/screenlock_bridge.h b/components/proximity_auth/screenlock_bridge.h
index 838637050846e6d2011f71f62436793524f9e23b..b1b37b63fa7ae33cb7c101bc0051d6250cabe0ef 100644
--- a/components/proximity_auth/screenlock_bridge.h
+++ b/components/proximity_auth/screenlock_bridge.h
@@ -14,6 +14,8 @@
 #include "base/strings/string16.h"
 #include "base/values.h"
 
+#include "components/user_manager/user_id.h"
+
 namespace content {
 class BrowserContext;
 }  // namespace content
@@ -114,31 +116,31 @@ class ScreenlockBridge {
 
     // Shows a custom icon in the user pod on the lock screen.
     virtual void ShowUserPodCustomIcon(
-        const std::string& user_email,
+        const user_manager::UserID& user_id,
         const UserPodCustomIconOptions& icon) = 0;
 
     // Hides the custom icon in user pod for a user.
-    virtual void HideUserPodCustomIcon(const std::string& user_email) = 0;
+    virtual void HideUserPodCustomIcon(const user_manager::UserID& user_id) = 0;
 
     // (Re)enable lock screen UI.
     virtual void EnableInput() = 0;
 
     // Set the authentication type to be used on the lock screen.
-    virtual void SetAuthType(const std::string& user_email,
+    virtual void SetAuthType(const user_manager::UserID& user_id,
                              AuthType auth_type,
                              const base::string16& auth_value) = 0;
 
     // Returns the authentication type used for a user.
-    virtual AuthType GetAuthType(const std::string& user_email) const = 0;
+    virtual AuthType GetAuthType(const user_manager::UserID& user_id) const = 0;
 
     // Returns the type of the screen -- a signin or a lock screen.
     virtual ScreenType GetScreenType() const = 0;
 
     // Unlocks from easy unlock app for a user.
-    virtual void Unlock(const std::string& user_email) = 0;
+    virtual void Unlock(const user_manager::UserID& user_id) = 0;
 
     // Attempts to login the user using an easy unlock key.
-    virtual void AttemptEasySignin(const std::string& user_email,
+    virtual void AttemptEasySignin(const user_manager::UserID& user_id,
                                    const std::string& secret,
                                    const std::string& key_label) = 0;
 
@@ -155,14 +157,14 @@ class ScreenlockBridge {
     virtual void OnScreenDidUnlock(LockHandler::ScreenType screen_type) = 0;
 
     // Invoked when the user focused on the lock screen changes.
-    virtual void OnFocusedUserChanged(const std::string& user_id) = 0;
+    virtual void OnFocusedUserChanged(const user_manager::UserID& user_id) = 0;
 
    protected:
     virtual ~Observer() {}
   };
 
   void SetLockHandler(LockHandler* lock_handler);
-  void SetFocusedUser(const std::string& user_id);
+  void SetFocusedUser(const user_manager::UserID& user_id);
 
   bool IsLocked() const;
   void Lock(content::BrowserContext* browser_context);
@@ -173,13 +175,13 @@ class ScreenlockBridge {
 
   LockHandler* lock_handler() { return lock_handler_; }
 
-  std::string focused_user_id() const { return focused_user_id_; }
+  const user_manager::UserID& focused_user_id() const { return focused_user_id_; }
 
  private:
   ProximityAuthClient* client_;  // Not owned. Must outlive this object.
   LockHandler* lock_handler_;    // Not owned
   // The last focused user's id.
-  std::string focused_user_id_;
+  user_manager::UserID focused_user_id_;
   ObserverList<Observer, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenlockBridge);