scroll_(evt) {
    var fieldset = this.getElement().querySelector('fieldset');
    var position = goog.style.getPosition(fieldset);

    var newY = position.y - evt.deltaY * 5;
    // Set upper boundary.
    newY = Math.min(0, newY);
    // Set lower boundary.
    newY = Math.max(window.innerHeight * -1, newY);

    goog.style.setPosition(fieldset, 0, newY);
  }
Scrolls the looking glass up/down.
@param {goog.events.MouseWheelEvent} evt The mouse wheel event to
    scroll up/down.
@private