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

chrome/browser/resources/settings/controls/settings_idle_render.js

 // Copyright 2017 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
  * settings-idle-render is a simple variant of dom-if designed for lazy
  * rendering of elements that are accessed imperatively.
  * If a use for idle time expansion is found outside of settings, this code
  * should be replaced by cr-lazy-render after that feature is merged into
@@ skipping 12 matching lines @@
   /** @private {number} */
   idleCallback_: 0,
 
   /** @override */
   attached: function() {
     this.idleCallback_ = requestIdleCallback(this.render_.bind(this));
   },
 
   /** @override */
   detached: function() {
+    this.child_ = null;

[Dan Beam, 2017/02/11 23:01:35]

but wait, does this mean it could get double-rendered?

can we maybe rename child_ to something less cryptic?

[tsergeant, 2017/02/15 06:31:39]

Yeah, if you detach the settings-idle-render, its internal state is reset to
having no child, but that child can still be rendered and attached to the DOM
tree.

dom-if handles this by ensuring that the rendered template instance is destroyed
when the template is detached:

https://github.com/Polymer/polymer/blob/6fc567fbf4e69ab1be2623212d5254eb38515...

     // No-op if callback already fired.
     cancelIdleCallback(this.idleCallback_);
   },
 
   /**
    * 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_)
@@ skipping 24 matching lines @@
 
   /**
    * @param {string} path
    * @param {Object} value
    */
   _forwardParentPath: function(path, value) {
     if (this.child_)
       this.child_._templateInstance.notifyPath(path, value, true);
   }
 });