We should replace CSSStyleSheet's setParentRule() by clearParentRule() to enforce the fact that CSSStyleSheet can't be moved to another parent rule after creation.
Created attachment 117835 [details] Patch
Comment on attachment 117835 [details] Patch The pach looks good. I am unfamiliar with the naming preference owner/parentRule but that seem consistent with CSSOM.
Comment on attachment 117835 [details] Patch Clearing flags on attachment: 117835 Committed r101972: <http://trac.webkit.org/changeset/101972>
All reviewed patches have been landed. Closing bug.