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

ash/wm/power_button_controller.cc

Index: ash/wm/power_button_controller.cc
diff --git a/ash/wm/power_button_controller.cc b/ash/wm/power_button_controller.cc
index 628fc5d9438e4a46dd9ecc689a4c4d5b7f6df955..1ea1ec7a712b21df804cb97d8a4f161a86dfc366 100644
--- a/ash/wm/power_button_controller.cc
+++ b/ash/wm/power_button_controller.cc
@@ -196,4 +196,9 @@ void PowerButtonController::PowerButtonEventReceived(
   OnPowerButtonEvent(down, timestamp);
 }
 
+void PowerButtonController::ResetTabletPowerButtonControllerForTest() {
+  tablet_controller_.reset(
+      new TabletPowerButtonController(lock_state_controller_));
+}
+
 }  // namespace ash