They render to a texture, send the texture ID to the compositor, and that ID is absolutely meaningless because we didn't set up resource sharing. D'oh!
THis is PR 151063 internally
Created attachment 145159 [details]
Comment on attachment 145159 [details]
Clearing flags on attachment: 145159
Committed r119185: <http://trac.webkit.org/changeset/119185>
All reviewed patches have been landed. Closing bug.