function initSeamlessField(innerHTML, styles) {
  const field = new SeamlessField('field');
  fieldElem.innerHTML = innerHTML;
  style.setStyle(fieldElem, styles);
  return field;
}
Initialize a new editable field for the field id 'field', with the given
innerHTML and styles.
@param {string} innerHTML html for the field contents.
@param {?Object} styles Key-value pairs for styles on the field.
@return {!SeamlessField} The field.