XMLHttpRequest properties should be on the prototype, like other interfaces. This should be possible now that Bug 134364 has been fixed and attributes on the prototype are now configurable.
Created attachment 261748 [details] Patch
Comment on attachment 261748 [details] Patch Clearing flags on attachment: 261748 Committed r190123: <http://trac.webkit.org/changeset/190123>
All reviewed patches have been landed. Closing bug.