Update Polymer components.

third_party/polymer/components/paper-styles/element-styles/paper-item-styles.html

 <!--
 @license
 Copyright (c) 2017 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="../../polymer/polymer.html">
 <link rel="import" href="../color.html">
 <link rel="import" href="../default-theme.html">
 <link rel="import" href="../typography.html">
 
 <!--
 Material design: [Lists](https://www.google.com/design/spec/components/lists.html)
 
 Shared styles for a native `button` to be used as an item in a `paper-listbox` element:
 
     <custom-style>
-      <style is="custom-style" include="paper-item"></style>
+      <style is="custom-style" include="paper-item-styles"></style>
     </custom-style>
 
     <paper-listbox>
       <button class="paper-item" role="option">Inbox</button>
       <button class="paper-item" role="option">Starred</button>
       <button class="paper-item" role="option">Sent mail</button>
     </paper-listbox>
 
 @group Paper Elements
 @demo demo/index.html
 -->
 
-<dom-module id="paper-item">
+<dom-module id="paper-item-styles">
   <template>
     <style>
       :host, html {
         --paper-item: {
           display: block;
           position: relative;
           min-height: var(--paper-item-min-height, 48px);
           padding: 0px 16px;
           @apply --paper-font-subhead;
           border:none;
@@ skipping 35 matching lines @@
         bottom: 0;
         background: currentColor;
         content: '';
         opacity: var(--dark-divider-opacity);
         pointer-events: none;
         @apply --paper-item-focused-before;
       }
     </style>
   </template>
 </dom-module>