Write tests for input elements supplying name by aria-labelledby

[extra808]

Regardless of how an input element is named (implicit or explicit <label>, aria-label, aria-labelledby, etc.), or its input type, if another element references it using aria-labelledby, that name should be supplied.

Example, both elements, button and input, should be read as "Check A" by assistive technologies:

<button aria-labelledby="check-a"></button> <input id="check-a" type="checkbox"> <label for="check-a">Check A</label>

Related WebKit (on macOS) bug: 284774