When an optgroup element became 'disabled' or not-'disabled', distribution should happen.

Since an optgroup element does not create a renderer, we cannot check this using reftest.

PASS nodes1.length is 1
PASS nodes1.item(0).innerHTML is "optgroup 2"
PASS nodes2.length is 1
PASS nodes2.item(0).innerHTML is "optgroup 3"
PASS successfullyParsed is true

TEST COMPLETE