cros: Update touchscreen status with backlights forced off state during start

ash/system/power/tablet_power_button_controller.h

 // 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.
 
 #ifndef ASH_SYSTEM_POWER_TABLET_POWER_BUTTON_CONTROLLER_H_
 #define ASH_SYSTEM_POWER_TABLET_POWER_BUTTON_CONTROLLER_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 74 matching lines @@
   // |forced_off|.
   void SetDisplayForcedOff(bool forced_off);
 
   // Sends a request to powerd to get the backlights forced off state so that
   // |backlights_forced_off_| can be initialized.
   void GetInitialBacklightsForcedOff();
 
   // Initializes |backlights_forced_off_|.
   void OnGotInitialBacklightsForcedOff(bool is_forced_off);
 
+  // Enables or disables the touchscreen, also writing its state to a pref in
+  // local state. The touchscreen is disabled when backlights are forced off.
+  void UpdateTouchscreenStatus();
+
   // Starts |shutdown_timer_| when the power button is pressed while in
   // tablet mode.
   void StartShutdownTimer();
 
   // Called by |shutdown_timer_| to start the pre-shutdown animation.
   void OnShutdownTimeout();
 
   // Locks the screen if the "require password to wake from sleep" pref is set
   // and locking is possible.
   void LockScreenIfRequired();
@@ skipping 27 matching lines @@
   LockStateController* controller_;  // Not owned.
 
   base::WeakPtrFactory<TabletPowerButtonController> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TabletPowerButtonController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_POWER_TABLET_POWER_BUTTON_CONTROLLER_H_