Add assignedElement to HTMLSlotElement (#3408)
Add assignedElement to HTMLSlotElement (#3408)

* Add assignedElement to HTMLSlotElement.

* Update api/HTMLSlotElement.json

Co-Authored-By: jpmedley <e5f32d9ca37888f2e401c8370536acae62d3b209@google.com>

chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,mdn/browser-compat-data