We should use shadowHost() instead of shadowAncestorNode(). Let's update the method name for preventing further use of shadowAncestorNode().
Created attachment 184133 [details] Patch
dglazkov is your man.
Comment on attachment 184133 [details] Patch Clearing flags on attachment: 184133 Committed r140541: <http://trac.webkit.org/changeset/140541>
All reviewed patches have been landed. Closing bug.