[Night Light] Accessibility: Make ChromeVox speak button status on toggles

ash/system/night_light/night_light_toggle_button.h

 // 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.
 
 #ifndef ASH_SYSTEM_NIGHT_LIGHT_NIGHT_LIGHT_TOGGLE_BUTTON_H_
 #define ASH_SYSTEM_NIGHT_LIGHT_NIGHT_LIGHT_TOGGLE_BUTTON_H_
 
 #include "ash/system/tray/system_menu_button.h"
 #include "base/macros.h"
 
 namespace ash {
 
 // The NightLight toggle button in the system tray.
 class NightLightToggleButton : public SystemMenuButton {
  public:
   explicit NightLightToggleButton(views::ButtonListener* listener);
   ~NightLightToggleButton() override = default;
 
+  // Toggles the status of NightLight.
+  void Toggle();
+
+ private:
   // Updates the icon and its style based on the status of NightLight.
   void Update();
 
- private:
   // views::View:
   void GetAccessibleNodeData(ui::AXNodeData* node_data) override;
 
   DISALLOW_COPY_AND_ASSIGN(NightLightToggleButton);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_NIGHT_LIGHT_NIGHT_LIGHT_TOGGLE_BUTTON_H_