Hide Night Light behind a flag

ash/system/tiles/tray_tiles_unittest.cc

Index: ash/system/tiles/tray_tiles_unittest.cc
diff --git a/ash/system/tiles/tray_tiles_unittest.cc b/ash/system/tiles/tray_tiles_unittest.cc
index 7341f72566050af1302add213ae340d0d5eb6e0c..6599f489efac6c25e8957c5ef28cdfbbf887182a 100644
--- a/ash/system/tiles/tray_tiles_unittest.cc
+++ b/ash/system/tiles/tray_tiles_unittest.cc
@@ -4,11 +4,14 @@
 
 #include "ash/system/tiles/tray_tiles.h"
 
+#include "ash/ash_switches.h"
+#include "ash/system/night_light/night_light_controller.h"
 #include "ash/system/night_light/night_light_toggle_button.h"
 #include "ash/system/tiles/tiles_default_view.h"
 #include "ash/system/tray/system_menu_button.h"
 #include "ash/test/ash_test_base.h"
 #include "ash/test/test_session_controller_client.h"
+#include "base/command_line.h"
 #include "components/user_manager/user_type.h"
 #include "ui/views/view.h"
 
@@ -23,6 +26,10 @@ class TrayTilesTest : public test::NoSessionAshTestBase {
   ~TrayTilesTest() override {}
 
   void SetUp() override {
+    // Explicitly enable the NightLight feature for the tests.
+    base::CommandLine::ForCurrentProcess()->AppendSwitch(
+        ash::switches::kAshEnableNightLight);
+
     test::NoSessionAshTestBase::SetUp();
     tray_tiles_.reset(new TrayTiles(GetPrimarySystemTray()));
   }