Hide Night Light behind a flag

ash/system/night_light/night_light_controller_unittest.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 <cmath>
 #include <limits>
 
 #include "ash/public/cpp/ash_pref_names.h"
@@ skipping 58 matching lines @@
 
   TestingPrefServiceSimple* user1_pref_service() {
     return &user1_pref_service_;
   }
   TestingPrefServiceSimple* user2_pref_service() {
     return &user2_pref_service_;
   }
 
   // ash::test::AshTestBase:
   void SetUp() override {
+    // Explicitly enable the NightLight feature for the tests.
+    NightLightController::EnableFeatureForTesting();
+
     test::AshTestBase::SetUp();
     CreateTestUserSessions();
     Shell::RegisterPrefs(user1_pref_service_.registry());
     Shell::RegisterPrefs(user2_pref_service_.registry());
 
     // Simulate user 1 login.
     InjectTestPrefService(&user1_pref_service_);
     SwitchActiveUser(kUser1Email);
   }
 
@@ skipping 152 matching lines @@
   user1_pref_service()->SetDouble(prefs::kNightLightTemperature, temperature2);
   EXPECT_EQ(temperature2, controller->GetColorTemperature());
   EXPECT_TRUE(TestLayersTemperature(temperature2));
   user1_pref_service()->SetBoolean(prefs::kNightLightEnabled, false);
   EXPECT_FALSE(controller->GetEnabled());
 }
 
 }  // namespace
 
 }  // namespace ash