[Night Light] CL2: Ash and system tray work

ash/system/night_light/tray_night_light.cc

Index: ash/system/night_light/tray_night_light.cc
diff --git a/ash/system/night_light/tray_night_light.cc b/ash/system/night_light/tray_night_light.cc
new file mode 100644
index 0000000000000000000000000000000000000000..bbd64b3a0a19ba81651372f1752a6b6c8e109295
--- /dev/null
+++ b/ash/system/night_light/tray_night_light.cc
@@ -0,0 +1,31 @@
+// 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/tray_night_light.h"
+
+#include "ash/resources/vector_icons/vector_icons.h"
+#include "ash/shell.h"
+#include "ui/views/view.h"
+
+namespace ash {
+
+TrayNightLight::TrayNightLight(SystemTray* system_tray)
+    : TrayImageItem(system_tray, kSystemTrayNightLightIcon, UMA_NIGHT_LIGHT) {
+  Shell::Get()->night_light_controller()->AddObserver(this);
+}
+
+TrayNightLight::~TrayNightLight() {
+  Shell::Get()->night_light_controller()->RemoveObserver(this);
+}
+
+void TrayNightLight::OnNightLightEnabledChanged(bool enabled) {
+  if (tray_view())
+    tray_view()->SetVisible(enabled);
+}
+
+bool TrayNightLight::GetInitialVisibility() {
+  return Shell::Get()->night_light_controller()->enabled();
+}
+
+}  // namespace ash