Hide Night Light behind a flag

ash/system/night_light/night_light_controller.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/system/night_light/night_light_controller.h"
 
+#include "ash/ash_switches.h"
 #include "ash/public/cpp/ash_pref_names.h"
 #include "ash/session/session_controller.h"
 #include "ash/shell.h"
+#include "base/command_line.h"
 #include "base/time/time.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/pref_service.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
 
 namespace ash {
 
 namespace {
 
@@ skipping 30 matching lines @@
     SessionController* session_controller)
     : session_controller_(session_controller) {
   session_controller_->AddObserver(this);
 }
 
 NightLightController::~NightLightController() {
   session_controller_->RemoveObserver(this);
 }
 
 // static
+bool NightLightController::IsFeatureEnabled() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      ash::switches::kAshEnableNightLight);
+}
+
+// static
 void NightLightController::RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterBooleanPref(prefs::kNightLightEnabled, false);
   registry->RegisterDoublePref(prefs::kNightLightTemperature,
                                kDefaultColorTemperature);
 }
 
 void NightLightController::AddObserver(Observer* observer) {
   observers_.AddObserver(observer);
 }
 
@@ skipping 84 matching lines @@
   Refresh();
   NotifyStatusChanged();
 }
 
 void NightLightController::OnColorTemperaturePrefChanged() {
   DCHECK(active_user_pref_service_);
   Refresh();
 }
 
 }  // namespace ash