cros:Ensure sys tray on secondary screen shows

We hide the sys tray on the secondary screen when showing
the lock screen that allows users to add a second user.

We never show the sys tray again, so fix this.

Bug: 1189358
Change-Id: Id4596ff4ae355e20931250dcf10c08f804e74bd7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2800474
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#868687}

diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index f5847cf..32bfd480 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc

@@ -486,6 +486,7 @@
 
   // Still handle it to avoid crashes during Login/Lock/Unlock flows.
   authentication_stage_ = AuthenticationStage::kIdle;
+  SetSystemTrayVisibility(SystemTrayVisibility::kAll);
 }
 
 void LoginScreenController::NotifyLoginScreenShown() {