Send screen on and off state as a11y alert

ash/system/chromeos/power/tablet_power_button_controller.cc

 // Copyright 2016 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/chromeos/power/tablet_power_button_controller.h"
 
+#include "ash/common/accessibility_delegate.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/wm/maximize_mode/maximize_mode_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ash/shell.h"
 #include "ash/wm/lock_state_controller.h"
 #include "base/time/default_tick_clock.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "ui/events/devices/input_device_manager.h"
 #include "ui/events/devices/stylus_state.h"
 #include "ui/events/event.h"
@@ skipping 151 matching lines @@
 }
 
 void TabletPowerButtonController::SetBacklightsForcedOff(bool forced_off) {
   if (backlights_forced_off_ == forced_off)
     return;
 
   chromeos::DBusThreadManager::Get()
       ->GetPowerManagerClient()
       ->SetBacklightsForcedOff(forced_off);
   backlights_forced_off_ = forced_off;
+
+  // Send an a11y alert.
+  WmShell::Get()->accessibility_delegate()->TriggerAccessibilityAlert(
+      forced_off ? A11Y_ALERT_SCREEN_OFF : A11Y_ALERT_SCREEN_ON);
 }
 
 void TabletPowerButtonController::GetInitialBacklightsForcedOff() {
   chromeos::DBusThreadManager::Get()
       ->GetPowerManagerClient()
       ->GetBacklightsForcedOff(base::Bind(
           &TabletPowerButtonController::OnGotInitialBacklightsForcedOff,
           weak_ptr_factory_.GetWeakPtr()));
 }
 
@@ skipping 17 matching lines @@
       WmShell::Get()->GetSessionStateDelegate();
   if (session_state_delegate->ShouldLockScreenAutomatically() &&
       session_state_delegate->CanLockScreen() &&
       !session_state_delegate->IsUserSessionBlocked() &&
       !controller_->LockRequested()) {
     session_state_delegate->LockScreen();
   }
 }
 
 }  // namespace ash