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

chrome/browser/supervised_user/supervised_user_constants.cc

Index: chrome/browser/supervised_user/supervised_user_constants.cc
diff --git a/chrome/browser/supervised_user/supervised_user_constants.cc b/chrome/browser/supervised_user/supervised_user_constants.cc
index 79a89dc2774acae013f4621b8e7c246bfe311165..6f18313636451677d5da96683f88c5dac7505f67 100644
--- a/chrome/browser/supervised_user/supervised_user_constants.cc
+++ b/chrome/browser/supervised_user/supervised_user_constants.cc
@@ -3,6 +3,11 @@
 // found in the LICENSE file.
 
 #include "chrome/browser/supervised_user/supervised_user_constants.h"
+#include "components/user_manager/user_id.h"
+
+namespace {
+  const char kChildAccountSUID[] = "ChildAccountSUID";
+}
 
 namespace supervised_users {
 
@@ -19,11 +24,13 @@ const char kUserName[] = "UserName";
 
 const char kSupervisedUserPseudoEmail[] = "managed_user@localhost";
 
-const char kChildAccountSUID[] = "ChildAccountSUID";
-
 const char kChromeAvatarIndex[] = "chrome-avatar-index";
 const char kChromeOSAvatarIndex[] = "chromeos-avatar-index";
 
 const char kChromeOSPasswordData[] = "chromeos-password-data";
 
+user_manager::UserID GetChildAccountSUID() {
+ return user_manager::UserID::FromUserEmail(kChildAccountSUID);
+}
+
 }  // namespace supervised_users