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

chrome/browser/profiles/profile_info_cache.cc

Index: chrome/browser/profiles/profile_info_cache.cc
diff --git a/chrome/browser/profiles/profile_info_cache.cc b/chrome/browser/profiles/profile_info_cache.cc
index e80e0304a4f78b564b1f23f672230c73931bf196..3041439c216698ab43db7d3298ce13d7851d99d2 100644
--- a/chrome/browser/profiles/profile_info_cache.cc
+++ b/chrome/browser/profiles/profile_info_cache.cc
@@ -26,6 +26,7 @@
 #include "chrome/common/pref_names.h"
 #include "chrome/grit/generated_resources.h"
 #include "components/signin/core/common/profile_management_switches.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/browser/browser_thread.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
@@ -201,7 +202,7 @@ void ProfileInfoCache::AddProfileToCache(
     const std::string& gaia_id,
     const base::string16& user_name,
     size_t icon_index,
-    const std::string& supervised_user_id) {
+    const user_manager::UserID& supervised_user_id) {
   std::string key = CacheKeyFromProfilePath(profile_path);
   DictionaryPrefUpdate update(prefs_, prefs::kProfileInfoCache);
   base::DictionaryValue* cache = update.Get();
@@ -214,7 +215,7 @@ void ProfileInfoCache::AddProfileToCache(
       profiles::GetDefaultAvatarIconUrl(icon_index));
   // Default value for whether background apps are running is false.
   info->SetBoolean(kBackgroundAppsKey, false);
-  info->SetString(kSupervisedUserId, supervised_user_id);
+  info->SetString(kSupervisedUserId, supervised_user_id.GetUserEmail());
   info->SetBoolean(kIsOmittedFromProfileListKey, !supervised_user_id.empty());
   info->SetBoolean(kProfileIsEphemeral, false);
   info->SetBoolean(kIsUsingDefaultNameKey, IsDefaultProfileName(name));
@@ -414,7 +415,7 @@ bool ProfileInfoCache::ProfileIsSupervisedAtIndex(size_t index) const {
 bool ProfileInfoCache::ProfileIsChildAtIndex(size_t index) const {
 #if defined(ENABLE_SUPERVISED_USERS)
   return GetSupervisedUserIdOfProfileAtIndex(index) ==
-      supervised_users::kChildAccountSUID;
+      supervised_users::GetChildAccountSUID();
 #else
   return false;
 #endif
@@ -437,12 +438,12 @@ bool ProfileInfoCache::ProfileIsSigninRequiredAtIndex(size_t index) const {
   return value;
 }
 
-std::string ProfileInfoCache::GetSupervisedUserIdOfProfileAtIndex(
+user_manager::UserID ProfileInfoCache::GetSupervisedUserIdOfProfileAtIndex(
     size_t index) const {
-  std::string supervised_user_id;
+  std::string supervised_user_email;
   GetInfoForProfileAtIndex(index)->GetString(kSupervisedUserId,
-                                             &supervised_user_id);
-  return supervised_user_id;
+                                             &supervised_user_email);
+  return user_manager::UserID::FromUserEmail(supervised_user_email);
 }
 
 bool ProfileInfoCache::ProfileIsEphemeralAtIndex(size_t index) const {
@@ -602,12 +603,12 @@ void ProfileInfoCache::SetIsOmittedProfileAtIndex(size_t index,
 
 void ProfileInfoCache::SetSupervisedUserIdOfProfileAtIndex(
     size_t index,
-    const std::string& id) {
+    const user_manager::UserID& id) {
   if (GetSupervisedUserIdOfProfileAtIndex(index) == id)
     return;
   scoped_ptr<base::DictionaryValue> info(
       GetInfoForProfileAtIndex(index)->DeepCopy());
-  info->SetString(kSupervisedUserId, id);
+  info->SetString(kSupervisedUserId, id.GetUserEmail());
   // This takes ownership of |info|.
   SetInfoForProfileAtIndex(index, info.release());