// Retrieves gclid value from cookie and stores in hidden form field id='gclid_field'
<script>
  function readCookie(name) {
  var n = name + "=";
  var cookie = document.cookie.split(';');
  for(var i=0;i < cookie.length;i++) {
      var c = cookie[i];
      while (c.charAt(0)==' '){c = c.substring(1,c.length);}
      if (c.indexOf(n) == 0){return c.substring(n.length,c.length);}
  }
  return null;
  }

  window.onload = function() {
      document.getElementById('gclid_field').value =
  readCookie('gclid');
  }
  </script>