Just silently ignore them to avoid UI process crashes.
Created attachment 374209 [details] Patch
Thanks for the patch. If this patch contains new public API please make sure it follows the guidelines for new WebKit2 GTK+ API. See http://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Committed r247507: <https://trac.webkit.org/changeset/247507>