Tweak 'scroll' listener registration in CrScrollableBehavior.

ui/webui/resources/cr_elements/cr_scrollable_behavior.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 Behavior for scrollable containers with <iron-list>.
  *
  * Any containers with the 'scrollable' attribute set will have the following
  * classes toggled appropriately: can-scroll, is-scrolled, scrolled-to-bottom.
  * These classes are used to style the container div and list elements
@@ skipping 18 matching lines @@
  *   </template>
  * </dom-module>
  *
  * NOTE: If 'container' is not fixed size, it is important to call
  * updateScrollableContents() when [[items]] changes, otherwise the container
  * will not be sized correctly.
  */
 
 /** @polymerBehavior */
 var CrScrollableBehavior = {
-  attached: function() {
+  ready: function() {
     var scrollableElements = this.root.querySelectorAll('[scrollable]');
 
     // Setup the intial scrolling related classes for each scrollable container.
     requestAnimationFrame(function() {
       for (let scrollable of scrollableElements)
         this.updateScroll_(scrollable);
     }.bind(this));
 
     // Listen to the 'scroll' event for each scrollable container.
     for (let scrollable of scrollableElements)
       scrollable.addEventListener('scroll', this.updateScrollEvent_.bind(this));
   },
 
-  detached: function() {
-    // Remove 'scroll' event listeners.
-    var scrollableElements = this.root.querySelectorAll('[scrollable]');
-    for (let scrollable of scrollableElements) {
-      scrollable.removeEventListener(
-          'scroll', this.updateScrollEvent_.bind(this));
-    }
-  },
-
   /**
    * Called any time the contents of a scrollable container may have changed.
    * This ensures that the <iron-list> contents of dynamically sized
    * containers are resized correctly.
    */
   updateScrollableContents() {
     let nodeList = this.root.querySelectorAll('[scrollable] iron-list');
     // Use setTimeout to avoid initial render / sizing issues.
     let intervalId = setInterval(function() {
       let unreadyNodes = [];
@@ skipping 29 matching lines @@
    */
   updateScroll_(scrollable) {
     scrollable.classList.toggle(
         'can-scroll', scrollable.clientHeight < scrollable.scrollHeight);
     scrollable.classList.toggle('is-scrolled', scrollable.scrollTop > 0);
     scrollable.classList.toggle(
         'scrolled-to-bottom', scrollable.scrollTop + scrollable.clientHeight >=
             scrollable.scrollHeight);
   },
 };