[MD settings] handle being detached on cr-lazy-render and settings-idle-render

ui/webui/resources/cr_elements/cr_lazy_render/cr_lazy_render.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview
  * cr-lazy-render is a simple variant of dom-if designed for lazy rendering
  * of elements that are accessed imperatively.
  * Usage:
  *   <template is="cr-lazy-render" id="menu">
  *     <heavy-menu></heavy-menu>
  *   </template>
  *
  *   this.$.menu.get().show();
  */
 
 Polymer({
   is: 'cr-lazy-render',
   extends: 'template',
 
   behaviors: [Polymer.Templatizer],
 
   /** @private {TemplatizerNode} */
   child_: null,
 
+  /** @override */
+  detached: function() {
+    this.child_ = null;
+  },
+
   /**
    * Stamp the template into the DOM tree synchronously
    * @return {Element} Child element which has been stamped into the DOM tree.
    */
   get: function() {
     if (!this.child_)
       this.render_();
     return this.child_;
   },
 
@@ skipping 28 matching lines @@
 
   /**
    * @param {string} path
    * @param {Object} value
    */
   _forwardParentPath: function(path, value) {
     if (this.child_)
       this.child_._templateInstance.notifyPath(path, value, true);
   }
 });