Focus parent elements in the current page

[jdm]

Document::commit_focus_transaction mentions // Update the focus state for all elements in the focus chain. but only attempts to focus an enclosing iframe element; all other elements in the chain are ignored. This is visible tests/html/select.html from #7847 if the JS is changed to focus an <option> instead of a <select>; the CSS selector for focused <select> doesn't get applied, because the focus state is never set on the parent <select>.