The Compositing and Blending spec is now in CR, see: http://lists.w3.org/Archives/Public/public-fx/2014JanMar/0048.html background-blend-mode has been in the webkit codebase for over 6 months, has been quite stable and is not behind a compile time flag any more. We feel it's ready to remove the prefix as it is very unlikely that the behavior will change.
Created attachment 223333 [details] Patch V1
Comment on attachment 223333 [details] Patch V1 r+, but I wondered if we should keep the prefixed form around for a while.... although I guess at least Safari didn't ship with it.
Comment on attachment 223333 [details] Patch V1 Clearing flags on attachment: 223333 Committed r163633: <http://trac.webkit.org/changeset/163633>
All reviewed patches have been landed. Closing bug.