The missing paper-dropdown element of Polymer.
Install:
bower install --save Polymer-paper-dropdown
Usage:
<script src="/bower_components/platform/platform.js"></script>
<link rel="import" href="components/Polymer-paper-dropdown/paper-dropdown.html">
<paper-dropdown value="initValue" duration="300">
<paper-item value="itemValue1">item1</paper-item>
<paper-item value="itemValue2">item2</paper-item>
<paper-item value="itemValue3">item3</paper-item>
<paper-item value="itemValue4">item4</paper-item>
<paper-item value="itemValue5">item5</paper-item>
</paper-dropdown>