chrome/browser/resources/md_extensions/view_manager.html

<link rel="import" href="chrome://resources/html/polymer.html">

<link rel="import" href="chrome://resources/html/assert.html">
<link rel="import" href="chrome://resources/html/cr.html">

<dom-module id="extensions-view-manager">
  <template>
    <style>
      :host ::slotted([slot=view]) {
        bottom: 0;
        display: none;
        left: 0;
        position: absolute;
        right: 0;
        top: 0;
      }

      :host ::slotted(.active),
      :host ::slotted(.closing) {
        display: block;
      }
    </style>
    <slot name="view"></slot>
  </template>
  <script src="view_manager.js"></script>
</dom-module>