Import Polymer 0.8 and several key elements.

third_party/polymer/v0_8/components-chromium/iron-selector/test/content-element.html

+<!--
+Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+
+<link rel="import" href="../iron-selector.html">
+
+<dom-module id="test-content-element">
+
+  <template>
+
+    <iron-selector id="selector" selected="{{selected}}" selectable="[[selectable]]" attr-for-selected="id">
+      <content></content>
+    </iron-selector>
+
+  </template>
+
+</dom-module>
+
+<script>
+
+  Polymer({
+
+    is: 'test-content-element',
+
+    properties: {
+
+      selectable: String,
+
+      selected: {
+        type: String,
+        notify: true
+      }
+
+    }
+
+  });
+
+</script>