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

Make ChromeVox speak the status of the Night Light system tray button when
the button is pressed and the status is toggled.

BUG=706067

Review-Url: https://codereview.chromium.org/2965163002
Cr-Commit-Position: refs/heads/master@{#484948}

ash/system/night_light/night_light_toggle_button.cc

@@ -9,6 +9,7 @@
 #include "ash/system/night_light/night_light_controller.h"
 #include "ash/system/tray/tray_constants.h"
 #include "ash/system/tray/tray_popup_item_style.h"
+#include "ui/accessibility/ax_enums.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/gfx/paint_vector_icon.h"
@@ -54,6 +55,13 @@ NightLightToggleButton::NightLightToggleButton(views::ButtonListener* listener)
   Update();
 }
 
+void NightLightToggleButton::Toggle() {
+  DCHECK(NightLightController::IsFeatureEnabled());
+  Shell::Get()->night_light_controller()->Toggle();
+  Update();
+  NotifyAccessibilityEvent(ui::AX_EVENT_ARIA_ATTRIBUTE_CHANGED, true);
+}
+
 void NightLightToggleButton::Update() {
   const bool night_light_enabled =
       Shell::Get()->night_light_controller()->GetEnabled();

ash/system/night_light/night_light_toggle_button.h

@@ -16,10 +16,13 @@ class NightLightToggleButton : public SystemMenuButton {
   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;
 

ash/system/tiles/tiles_default_view.cc

@@ -126,8 +126,7 @@ void TilesDefaultView::ButtonPressed(views::Button* sender,
   } else if (NightLightController::IsFeatureEnabled() &&
              sender == night_light_button_) {
     Shell::Get()->metrics()->RecordUserMetricsAction(UMA_TRAY_NIGHT_LIGHT);
-    Shell::Get()->night_light_controller()->Toggle();
-    night_light_button_->Update();
+    night_light_button_->Toggle();
   } else if (sender == lock_button_) {
     Shell::Get()->metrics()->RecordUserMetricsAction(UMA_TRAY_LOCK_SCREEN);
     chromeos::DBusThreadManager::Get()