The check was called when the mouse was moved in a drag&drop operation.
Dragging all files in a directory with 3000 files under callgrind,
moving the mouse to the other panel and then canceling, doing it twice,
callgrind shows that the method urlListMatchesUrl was called around
200 times, spending around 9,30% of the cpu in those calls.
Applying the patch, the method is only called once, and callgrind tells
it uses less than 1% of the cpu in those calls.