function getChildNodes(node) {
  return genericPropertyGet(
      Methods.CHILD_NODES_GETTER, node, 'childNodes', function(childNodes) {
        return childNodes instanceof NodeList;
      });
}
Returns the value of node.childNodes without falling prey to things like
<form><input name="childNodes"></form>.
@param {!Node} node
@return {!NodeList<!Node>}