Form elements in Shadow DOM should work as described in the spec. The spec is here. https://dvcs.w3.org/hg/webcomponents/raw-file/tip/spec/shadow/index.html#html-forms
Created attachment 134544 [details] Patch
Comment on attachment 134544 [details] Patch ok.
Committed r112860: <http://trac.webkit.org/changeset/112860>