This issue was raised during review for https://codereview.chromium.org/2318873002

As per https://www.w3.org/TR/wai-aria/states_and_properties#aria-expanded

"If the element with the aria-expanded attribute controls the expansion of another grouping container that is not 'owned by' the element, the author SHOULD reference the container by using the aria-controls attribute."

Currently only JAWS screen reader supports this, and there is also lack of support for setting aria-controls across the shadow dom.

This issue is to track that we address it when there is better support for aria properties' interaction with the shadow dom.