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

ash/wm/power_button_controller.h

Index: ash/wm/power_button_controller.h
diff --git a/ash/wm/power_button_controller.h b/ash/wm/power_button_controller.h
index 989dd985dbcf8b3177b1ecda60c117298d79faf5..5669271572a8cb5b7bfc8f122c3925e4599e4392 100644
--- a/ash/wm/power_button_controller.h
+++ b/ash/wm/power_button_controller.h
@@ -52,6 +52,10 @@ class ASH_EXPORT PowerButtonController
   void PowerButtonEventReceived(bool down,
                                 const base::TimeTicks& timestamp) override;
 
+  // Resets |tablet_controller_| to hold a new object to simulate Chrome
+  // starting.
+  void ResetTabletPowerButtonControllerForTest();
+
   TabletPowerButtonController* tablet_power_button_controller_for_test() {
     return tablet_controller_.get();
   }