[proposal] add baseURI polyfill

[valdrinkoshi]

Would this be the right place where to add the polyfill for baseURI ?

if ('baseURI' in Node.prototype === false) {
  Object.defineProperty(Node.prototype, 'baseURI', {
    get: function() {
      var base = (this.ownerDocument || this).querySelector('base');
      return (base || window.location).href;
    },
    configurable: true,
    enumerable: true
  });
}