FormData should allow setting filename to empty
        https://bugs.webkit.org/show_bug.cgi?id=111687

        Reviewed by Brady Eidson.

        Tests: http/tests/local/formdata/send-form-data-with-empty-blob-filename.html
               http/tests/local/formdata/send-form-data-with-empty-file-filename.html

        * platform/network/FormData.cpp: (WebCore::FormData::appendKeyValuePairItems):
        Missing value is a null string. If the string is empty, we should treat is as
        authoritative.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145142 268f45cc-cd09-0410-ab3c-d52691b4dbfc