When an optgroup element became 'enabled' or not-'enabled', 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 1"
PASS nodes2.length is 1
PASS nodes2.item(0).innerHTML is "optgroup 4"
PASS successfullyParsed is true

TEST COMPLETE