styleAsDownloadButton = (button, attachPoint, iconText) => {
      attachPoint.classList.add('asset-card-corner-button');
      const icon = document.createElement('i');
      icon.textContent = iconText;
      icon.classList.add('material-icons-round');
      button.appendChild(icon);
    }
Makes the contents of the button into an MDL icon, and moves it into the
upper-right-hand corner with CSS styles.
@param {!Element} button
@param {!Element} attachPoint If there is no attach point, just pass the
 button in here.
@param {string} iconText