Código de my-app.html incluyendo el custom-element polymaiap-app

my-app.html

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<link rel="import" href="../bower_components/polymer/polymer.html">
<link rel="import" href="../bower_components/app-layout/app-drawer/app-drawer.html">
<link rel="import" href="../bower_components/app-layout/app-drawer-layout/app-drawer-layout.html">
<link rel="import" href="../bower_components/app-layout/app-header/app-header.html">
<link rel="import" href="../bower_components/app-layout/app-header-layout/app-header-layout.html">
<link rel="import" href="../bower_components/app-layout/app-scroll-effects/app-scroll-effects.html">
<link rel="import" href="../bower_components/app-layout/app-toolbar/app-toolbar.html">
<link rel="import" href="../bower_components/app-route/app-location.html">
<link rel="import" href="../bower_components/app-route/app-route.html">
<link rel="import" href="../bower_components/iron-pages/iron-pages.html">
<link rel="import" href="../bower_components/iron-selector/iron-selector.html">
<link rel="import" href="../bower_components/paper-icon-button/paper-icon-button.html">
<link rel="import" href="my-icons.html">

<dom-module id="polymaiap-app">
  <template>
    <style>
      :host {
        --app-primary-color: #4285f4;
        --app-secondary-color: black;
        display: block;
      }

      app-header {
        color: #fff;
        background-color: var(--app-primary-color);
      }
      app-header paper-icon-button {
        --paper-icon-button-ink-color: white;
      }

      .drawer-list {
        margin: 0 20px;
      }

      .drawer-list a {
        display: block;
        padding: 0 16px;
        text-decoration: none;
        color: var(--app-secondary-color);
        line-height: 40px;
      }

      .drawer-list a.iron-selected {
        color: black;
        font-weight: bold;
      }
    </style>

    <app-location route="{{route}}"></app-location>
    <app-route
        route="{{route}}"
        pattern="/:page"
        data="{{routeData}}"
        tail="{{subroute}}"></app-route>

    <app-drawer-layout fullbleed>
      <!-- Drawer content -->
      <app-drawer>
        <app-toolbar>Maiap Menu</app-toolbar>
        <iron-selector selected="[[page]]" attr-for-selected="name" class="drawer-list" role="navigation">
          <a name="list" href="/list" on-click="_toggleDrawer">Employees List</a>
        </iron-selector>
      </app-drawer>

      <!-- Main content -->
      <app-header-layout has-scrolling-region>

        <app-header condenses reveals effects="waterfall">
          <app-toolbar>
            <paper-icon-button icon="menu" drawer-toggle></paper-icon-button>
            <div main-title>Maiap</div>
          </app-toolbar>
        </app-header>

        <iron-pages
          selected="[[page]]"
          attr-for-selected="name"
          fallback-selection="404"
          role="main">
          <maiap-list name="list"></maiap-list>
          <maiap-employee name="employee" item="[[item]]" route="[[subroute]]"></maiap-employee>
          <error404 name="404"></error404>
        </iron-pages>
      </app-header-layout>
    </app-drawer-layout>
  </template>

  <script>
    Polymer({
      is: 'polymaiap-app',

      properties: {
        page: {
          type: String,
          reflectToAttribute: true,
          observer: '_pageChanged'
        },

        item: {
          type: Object
        }
      },

      listeners: {
        'selectedItem': '_onItemSelected'
      },

      observers: [
        '_routePageChanged(routeData.page)'
      ],

      _onItemSelected: function(event) {
        this.set('item', event.detail);
        this.set('route.path', '/employee/' + this.item.firstName);
      },

      _toggleDrawer: function() {
        this.$$('app-drawer').toggle();
      },

      _routePageChanged: function(page) {
        this.page = page || 'list';
      },

      _pageChanged: function(page) {
        // Load page import on demand. Show 404 page if fails
        var resolvedPageUrl = this.resolveUrl(page + '.html');
        this.importHref(resolvedPageUrl, null, this._showPage404, true);
      },

      _showPage404: function() {
        this.page = '404';
      }
    });
  </script>
</dom-module>