[Night Light] CL2: Ash and system tray work

ash/system/tray/system_tray.cc

Index: ash/system/tray/system_tray.cc
diff --git a/ash/system/tray/system_tray.cc b/ash/system/tray/system_tray.cc
index cc76d1068097efec0d4d5068776e8af061cd296a..08221599993a0847b2b358a3ef0cc7f193601ead 100644
--- a/ash/system/tray/system_tray.cc
+++ b/ash/system/tray/system_tray.cc
@@ -27,6 +27,7 @@
 #include "ash/system/media_security/multi_profile_media_tray_item.h"
 #include "ash/system/network/tray_network.h"
 #include "ash/system/network/tray_vpn.h"
+#include "ash/system/night_light/tray_night_light.h"
 #include "ash/system/power/power_status.h"
 #include "ash/system/power/tray_power.h"
 #include "ash/system/screen_security/screen_capture_tray_item.h"
@@ -273,6 +274,7 @@ void SystemTray::CreateItems(SystemTrayDelegate* delegate) {
   AddTrayItem(base::WrapUnique(tray_audio_));
   AddTrayItem(base::MakeUnique<TrayBrightness>(this));
   AddTrayItem(base::MakeUnique<TrayCapsLock>(this));
+  AddTrayItem(base::MakeUnique<TrayNightLight>(this));
   // TODO(jamescook): Remove this when mus has support for display management
   // and we have a DisplayManager equivalent. See http://crbug.com/548429
   std::unique_ptr<SystemTrayItem> tray_rotation_lock =