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

chrome/browser/signin/easy_unlock_service.h

Index: chrome/browser/signin/easy_unlock_service.h
diff --git a/chrome/browser/signin/easy_unlock_service.h b/chrome/browser/signin/easy_unlock_service.h
index db96b87c410f1187c31d1c056865d7e583043095..7b874d4a5ad6e3894e1d5a1a48ea41ed515c1024 100644
--- a/chrome/browser/signin/easy_unlock_service.h
+++ b/chrome/browser/signin/easy_unlock_service.h
@@ -18,6 +18,7 @@
 #include "chrome/browser/signin/easy_unlock_screenlock_state_handler.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/proximity_auth/screenlock_state.h"
+#include "components/user_manager/user_id.h"
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/login/easy_unlock/easy_unlock_types.h"
@@ -82,10 +83,10 @@ class EasyUnlockService : public KeyedService {
   static void RegisterPrefs(PrefRegistrySimple* registry);
 
   // Removes the hardlock state for the given user.
-  static void ResetLocalStateForUser(const std::string& user_id);
+  static void ResetLocalStateForUser(const user_manager::UserID& user_id);
 
   // Returns the user's preferences.
-  static UserSettings GetUserSettings(const std::string& user_id);
+  static UserSettings GetUserSettings(const user_manager::UserID& user_id);
 
   // Returns the identifier for the device.
   static std::string GetDeviceId();
@@ -97,7 +98,7 @@ class EasyUnlockService : public KeyedService {
   virtual Type GetType() const = 0;
 
   // Returns the user currently associated with the service.
-  virtual std::string GetUserEmail() const = 0;
+  virtual user_manager::UserID GetUserID() const = 0;
 
   // Launches Easy Unlock setup app.
   virtual void LaunchSetup() = 0;
@@ -131,11 +132,11 @@ class EasyUnlockService : public KeyedService {
   virtual std::string GetWrappedSecret() const = 0;
 
   // Records metrics for Easy sign-in outcome for the given user.
-  virtual void RecordEasySignInOutcome(const std::string& user_id,
+  virtual void RecordEasySignInOutcome(const user_manager::UserID& user_id,
                                        bool success) const = 0;
 
   // Records metrics for password based flow for the given user.
-  virtual void RecordPasswordLoginEvent(const std::string& user_id) const = 0;
+  virtual void RecordPasswordLoginEvent(const user_manager::UserID& user_id) const = 0;
 
   // Starts auto pairing.
   typedef base::Callback<void(bool success, const std::string& error)>
@@ -182,12 +183,12 @@ class EasyUnlockService : public KeyedService {
 
   // Starts an auth attempt for the user associated with the service. The
   // attempt type (unlock vs. signin) will depend on the service type.
-  void AttemptAuth(const std::string& user_id);
+  void AttemptAuth(const user_manager::UserID& user_id);
 
   // Similar to above but a callback is invoked after the auth attempt is
   // finalized instead of default unlock/sign-in.
   typedef EasyUnlockAuthAttempt::FinalizedCallback AttemptAuthCallback;
-  void AttemptAuth(const std::string& user_id,
+  void AttemptAuth(const user_manager::UserID& user_id,
                    const AttemptAuthCallback& callback);
 
   // Finalizes the previously started auth attempt for easy unlock. If called on
@@ -201,7 +202,7 @@ class EasyUnlockService : public KeyedService {
   void FinalizeSignin(const std::string& secret);
 
   // Handles Easy Unlock auth failure for the user.
-  void HandleAuthFailure(const std::string& user_id);
+  void HandleAuthFailure(const user_manager::UserID& user_id);
 
   // Checks the consistency between pairing data and cryptohome keys. Set
   // hardlock state if the two do not match.
@@ -284,7 +285,7 @@ class EasyUnlockService : public KeyedService {
   // Saves hardlock state for the given user. Update UI if the currently
   // associated user is the same.
   void SetHardlockStateForUser(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       EasyUnlockScreenlockStateHandler::HardlockState state);
 
   // Returns the authentication event for a recent password sign-in or unlock,
@@ -310,7 +311,7 @@ class EasyUnlockService : public KeyedService {
 #if defined(OS_CHROMEOS)
   // Callback for get key operation from CheckCryptohomeKeysAndMaybeHardlock.
   void OnCryptohomeKeysFetchedForChecking(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       const std::set<std::string> paired_devices,
       bool success,
       const chromeos::EasyUnlockDeviceKeyDataList& key_data_list);