code: function assumeButtonFocus(element, button) {
    button.addEventListener('mousedown', event => {
      // Given the main element the focus if it doesn't already have it.
      element.focus();
      // Prevent the default focus-on-mousedown behavior.
      event.preventDefault();
    });
  }
docs: /*
  By default, a button will always take focus on mousedown. For this component,
  we want to override that behavior, such that a mousedown on a button keeps
  the focus on the outer component.