Comment 2 for bug 1302740

The issue here is that delegating navigations to the browser behaves differently depending on whether the window has an opener or not (I'm not sure why). If a window doesn't have an opener, we get all top-level navigations. If it does have an opener, then we only get cross-domain navigations. When calling window.open() without support for creating new windows, blink sets window.opener on the top-level window (like it would for a newly created window) before calling in to content.