Bug 1578652 - Add a comment pointing to a gross gtk resize workaround. r=stransky

This was fixed upstream, so we can eventually remove this.

Having the issue number makes it much nicer to figure out when is the right time
to remove it.

Differential Revision: https://phabricator.services.mozilla.com/D44624

--HG--
extra : moz-landing-system : lando

widget/gtk/nsWindow.cpp

@@ -3242,6 +3242,8 @@ void nsWindow::OnWindowStateEvent(GtkWidget* aWidget,
   //
   // We instead notify gtk_window_state_event() of the maximized state change
   // once the window is shown.
+  //
+  // See https://gitlab.gnome.org/GNOME/gtk/issues/1044
   if (!mIsShown) {
     aEvent->changed_mask = static_cast<GdkWindowState>(
         aEvent->changed_mask & ~GDK_WINDOW_STATE_MAXIMIZED);