Create the control buttons on a notification when showing the buttons if needed.

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 39c3c6e4337eb5797c2e18d6bbb02ad7862aee98..cbba6a57f4bb780936ece454e561d545a9234fe6 100644
--- a/ui/arc/notification/arc_custom_notification_view.cc
+++ b/ui/arc/notification/arc_custom_notification_view.cc
@@ -342,9 +342,16 @@ void ArcCustomNotificationView::UpdatePreferredSize() {
 }
 
 void ArcCustomNotificationView::UpdateControlButtonsVisibility() {
-  if (!surface_ || !floating_control_buttons_widget_)
+  if (!surface_)
     return;
 
+  if (!floating_control_buttons_widget_) {
+    if (GetWidget())
+      CreateFloatingControlButtons();
+    else
+      return;
+  }
+
   const bool target_visiblity =
       IsMouseHovered() || (close_button_ && close_button_->HasFocus()) ||
       (settings_button_ && settings_button_->HasFocus());