rebase = new Firebase(form.getAttribute('action'));
      firebase.set(form.serializeForm());
    });

Note that if you're dynamically creating this element, it's mandatory that you
first create the contained `<form>` element and all its children, and only then
attach it to the `<iron-form>`:

  var wrapper = document.createElement('iron-form');
  var form = document.createElement('form');
  var input = document.createElement('input');
  form.appendChild(input);
  document.body.appendChild(wrapper);
  wrapp