Cancel menu showing animation only if menu is opened.

Bug: 826005
Change-Id: I237dbf4ae50b02a225110fa72dc0bb0c0127535f
Reviewed-on: https://chromium-review.googlesource.com/993755
Commit-Queue: Min Chen <minch@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547854}

ash/system/power/power_button_controller.cc

@@ -260,7 +260,8 @@ void PowerButtonController::OnPowerButtonEvent(
 
     // Cancel the menu animation if it's still ongoing when the button is
     // released on a clamshell device.
-    if (!ShouldTurnScreenOffForTap() && !show_menu_animation_done_) {
+    if (!ShouldTurnScreenOffForTap() && IsMenuOpened() &&
+        !show_menu_animation_done_) {
       static_cast<PowerButtonMenuScreenView*>(menu_widget_->GetContentsView())
           ->ScheduleShowHideAnimation(false);
     }