Make SkyElement more classy.

sky/examples/file-browser.sky

 <!--
 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 -->
 <import src="../framework/sky-element/sky-element.sky" as="SkyElement" />
 <import src="../framework/xmlhttprequest.sky" as="XMLHttpRequest" />
 
+<sky-element name="file-browser">
 <template>
   <style>
     heading {
       font-size: 16px;
     }
   </style>
   <heading>File browser for {{ url }}</heading>
   <template repeat="{{ directories }}">
     <a href="{{}}">{{}}</a>
   </template>
   <template repeat="{{ files }}">
     <a href="{{}}">{{}}</a>
   </template>
 </template>
 <script>
-SkyElement({
-  name: 'file-browser',
-  url: '',
-  files: [],
-  directories: [],
-  attached: function() {
+module.exports = class extends SkyElement {
+  created() {
+    this.url = '';
+    this.files = [];
+    this.directories = [];
+  }
+  attached() {
     this.url = this.ownerDocument.URL;
     var xhr = new XMLHttpRequest();
     xhr.open('GET', this.url + '?format=json');
     xhr.onload = (function() {
       var listing = JSON.parse(xhr.responseText);
       this.files = listing.files;
       this.directories = listing.directories;
     }).bind(this);
     xhr.send();
   }
-});
+}.register();
 </script>
+</sky-element>