Change in r134586 is not the problem, it indeed fixes the FIXME we have in the tests. The problem is that we were assuming that when no geometry is given to window.open() the default window rect is empty. This is not true anymore after r134586.
Created attachment 174927 [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 r135135: <http://trac.webkit.org/changeset/135135>