Ignore OnKeyEvent for VKEY_POWER because it is handled by PowerButtonEvent

ash/system/chromeos/power/tablet_power_button_controller.cc

Index: ash/system/chromeos/power/tablet_power_button_controller.cc
diff --git a/ash/system/chromeos/power/tablet_power_button_controller.cc b/ash/system/chromeos/power/tablet_power_button_controller.cc
index 3ee60e7e51576b87a1fb64cdf5ffb82ca61dbc50..06d9efae2292990d999ea471bae6c94bf3424912 100644
--- a/ash/system/chromeos/power/tablet_power_button_controller.cc
+++ b/ash/system/chromeos/power/tablet_power_button_controller.cc
@@ -139,6 +139,11 @@ void TabletPowerButtonController::SuspendDone(
 }
 
 void TabletPowerButtonController::OnKeyEvent(ui::KeyEvent* event) {
+  // Ignore key events generated by the power button since power button activity
+  // is already handled by OnPowerButtonEvent().
+  if (event->key_code() == ui::VKEY_POWER)
+    return;
+
   if (!IsTabletModeActive() && backlights_forced_off_)
     SetBacklightsForcedOff(false);
 }