The output file is never created, and shouldn't be. I think that the current behavior is to run the step unconditionally, and it doesn't make sense to make it more difficult.
Created attachment 246846 [details]
Comment on attachment 246846 [details]
Clearing flags on attachment: 246846
Committed r180313: <http://trac.webkit.org/changeset/180313>
All reviewed patches have been landed. Closing bug.