Update the button visibility when mouse enters or exits from notification surface window

ui/arc/notification/arc_custom_notification_view.cc

Index: ui/arc/notification/arc_custom_notification_view.cc
diff --git a/ui/arc/notification/arc_custom_notification_view.cc b/ui/arc/notification/arc_custom_notification_view.cc
index 6f145f732325bb3e899bfad4c27c609e6302f36c..2ea6ffef8f6abb476e9845e13c4bb5a582968c62 100644
--- a/ui/arc/notification/arc_custom_notification_view.cc
+++ b/ui/arc/notification/arc_custom_notification_view.cc
@@ -85,6 +85,12 @@ class ArcCustomNotificationView::EventForwarder : public ui::EventHandler {
       ui::LocatedEvent* located_event = event->AsLocatedEvent();
       located_event->target()->ConvertEventToTarget(widget->GetNativeWindow(),
                                                     located_event);
+      if (located_event->type() == ui::ET_MOUSE_ENTERED ||
+          located_event->type() == ui::ET_MOUSE_EXITED) {
+        owner_->UpdateControlButtonsVisibility();
+        return;
+      }
+
       if (located_event->type() == ui::ET_MOUSE_MOVED) {
         widget->OnMouseEvent(located_event->AsMouseEvent());
       } else if (located_event->IsScrollEvent()) {