function onPointerDown(e) {
      hadKeyboardEvent = false;
    }
If at any point a user clicks with a pointing device, ensure that we change
the modality away from keyboard.
This avoids the situation where a user presses a key on an already focused
element, and then clicks on a different element, focusing it with a
pointing device, while we still think we're in keyboard modality.
@param {Event} e