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

chrome/browser/chromeos/login/users/multi_profile_user_controller.h

Index: chrome/browser/chromeos/login/users/multi_profile_user_controller.h
diff --git a/chrome/browser/chromeos/login/users/multi_profile_user_controller.h b/chrome/browser/chromeos/login/users/multi_profile_user_controller.h
index 506794f9d8c780bb7fb9c2f7ecbb65ce1617d15c..9fa390bc55dbe81e63fd5cb4299805517d46945d 100644
--- a/chrome/browser/chromeos/login/users/multi_profile_user_controller.h
+++ b/chrome/browser/chromeos/login/users/multi_profile_user_controller.h
@@ -15,6 +15,10 @@ class PrefRegistrySimple;
 class PrefService;
 class Profile;
 
+namespace user_manager {
+class UserID;
+}
+
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
@@ -62,8 +66,8 @@ class MultiProfileUserController {
   static void RegisterPrefs(PrefRegistrySimple* registry);
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
-  // Returns the cached policy value for |user_email|.
-  std::string GetCachedValue(const std::string& user_email) const;
+  // Returns the cached policy value for |user_id|.
+  std::string GetCachedValue(const user_manager::UserID& user_id) const;
 
   // Returns primary user policy (only ALLOW,
   // NOT_ALLOWED_PRIMARY_POLICY_CERT_TAINTED,
@@ -72,14 +76,14 @@ class MultiProfileUserController {
 
   // Returns true if user allowed to be in the current session. If |reason| not
   // null stores UserAllowedInSessionReason enum that describes actual reason.
-  bool IsUserAllowedInSession(const std::string& user_email,
+  bool IsUserAllowedInSession(const user_manager::UserID& user_id,
                               UserAllowedInSessionReason* reason) const;
 
   // Starts to observe the multiprofile user behavior pref of the given profile.
   void StartObserving(Profile* user_profile);
 
   // Removes the cached values for the given user.
-  void RemoveCachedValues(const std::string& user_email);
+  void RemoveCachedValues(const user_manager::UserID& user_id);
 
   // Possible behavior values.
   static const char kBehaviorUnrestricted[];
@@ -91,7 +95,7 @@ class MultiProfileUserController {
   friend class MultiProfileUserControllerTest;
 
   // Sets the cached policy value.
-  void SetCachedValue(const std::string& user_email,
+  void SetCachedValue(const user_manager::UserID& user_id,
                       const std::string& behavior);
 
   // Checks if all users are allowed in the current session.