These are likely left behind from git. They do not cause any harm as far as I can tell, but we have quite a few of them (and I keep stumbling in them when just browsing/reading the code). At r136399, we have about 500 directories, most of them under ./LayoutTests/platform but a fair size under Source. Attached a list of empty directories and a small script to find them.
Created attachment 177502 [details] list of empty directories
Created attachment 177503 [details] script to find empty dirs in an svn repo
Yay, good proposal. ;) My dream is making "webkit-patch land" and CQ somehow remove empty directories automatically when you removed the files in them. Unfortunately it isn't trivial, because git can't handle empty directories at all. As far as I know we can only remove orphaned empty directories manually (and regularly).
Created attachment 193061 [details] Patch
I will resubmit the patch. Some error occurred while uploading patch with Tools/Scripts/webkit-patch upload. Remove empty directories details didn't come in patch.
Most if this was taken care by http://trac.webkit.org/changeset/148159 . Also see http://trac.webkit.org/changeset/154749 and http://trac.webkit.org/changeset/156827. Closing.