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..611d8c9c0ee0a2ca266549a8ba1be8644204bd2b 100644
--- a/ash/wm/power_button_controller.h
+++ b/ash/wm/power_button_controller.h
@@ -52,6 +52,8 @@ class ASH_EXPORT PowerButtonController
   void PowerButtonEventReceived(bool down,
                                 const base::TimeTicks& timestamp) override;
 
+  void ResetTabletPowerButtonControllerForTest();

[Daniel Erat, 2017/05/03 03:59:37]

nit: document what this does, e.g.

// Resets |tablet_controller_| to hold a new object to simulate
// Chrome starting.

[Qiang(Joe) Xu, 2017/05/03 04:17:33]

Done.

+
   TabletPowerButtonController* tablet_power_button_controller_for_test() {
     return tablet_controller_.get();
   }