This CL replaces std::string user_id in ash/* with AccountId.

ash/system/user/user_view.cc

Index: ash/system/user/user_view.cc
diff --git a/ash/system/user/user_view.cc b/ash/system/user/user_view.cc
index 0c48ca9977608d7b7a4c8cfc087faad88460231b..1b65bd586df12640cfc6f5a9339801462975b7b7 100644
--- a/ash/system/user/user_view.cc
+++ b/ash/system/user/user_view.cc
@@ -78,8 +78,7 @@ void SwitchUser(ash::UserIndex user_index) {
       ash::Shell::GetInstance()->session_state_delegate();
   ash::MultiProfileUMA::RecordSwitchActiveUser(
       ash::MultiProfileUMA::SWITCH_ACTIVE_USER_BY_TRAY);
-  delegate->SwitchActiveUser(
-      delegate->GetUserInfo(user_index)->GetAccountId().GetUserEmail());
+  delegate->SwitchActiveUser(delegate->GetUserInfo(user_index)->GetAccountId());
 }
 
 class LogoutButton : public TrayPopupLabelButton {