Chrome Version: 62 canary
OS: All but iOS

What steps will reproduce the problem?
(1) Open the following URL:
    data:text/html;charset=utf-8,<textarea%20autocomplete="on"></textarea><select%20autocomplete="on"></select><script>alert(document.querySelector('textarea').autocomplete%20+%20'%20/%20'%20+%20document.querySelector('select').autocomplete);</script>

What is the expected result?
Show show a dialog with "on / on".

What happens instead?
Show a dialog with "undefined / undefined".

Please use labels and text to provide additional information.
Safari implemented them. Edge and Firefox don't have.

Spec:
https://html.spec.whatwg.org/multipage/form-elements.html#the-select-element
https://html.spec.whatwg.org/multipage/form-elements.html#the-textarea-element
Test:
http://w3c-test.org/html/dom/reflection-forms.html

We already have autocomplete attribute support for SELECT and TEXTAREA. This issue is only for adding their IDL attributes.