WebUI: Undo some usages of ES6 features that break uglify.

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 28 matching lines @@
   properties: {
     /** @private {number|null} */
     intervalId_: {type: Number, value: null}
   },
 
   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);
+      for (var i = 0; i < scrollableElements.length; i++)
+        this.updateScroll_(scrollableElements[i]);
     }.bind(this));
 
     // Listen to the 'scroll' event for each scrollable container.
-    for (let scrollable of scrollableElements)
-      scrollable.addEventListener('scroll', this.updateScrollEvent_.bind(this));
+    for (var i = 0; i < scrollableElements.length; i++) {
+      scrollableElements[i].addEventListener(
+          'scroll', this.updateScrollEvent_.bind(this));
+    }
   },
 
   detached: function() {
     if (this.intervalId_ !== null)
       clearInterval(this.intervalId_);
   },
 
   /**
    * 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: function() {
     if (this.intervalId_ !== null)
       return;  // notifyResize is arelady in progress.
 
-    let nodeList = this.root.querySelectorAll('[scrollable] iron-list');
+    var nodeList = this.root.querySelectorAll('[scrollable] iron-list');
     // Use setInterval to avoid initial render / sizing issues.
     this.intervalId_ = window.setInterval(function() {
-      let unreadyNodes = [];
-      for (let node of nodeList) {
+      var unreadyNodes = [];
+      for (var i = 0; i < nodeList.length; i++) {
+        var node = nodeList[i];
         if (node.parentNode.scrollHeight == 0) {
           unreadyNodes.push(node);
           continue;
         }
-        let ironList = /** @type {!IronListElement} */ (node);
+        var ironList = /** @type {!IronListElement} */ (node);
         ironList.notifyResize();
       }
       if (unreadyNodes.length == 0) {
         window.clearInterval(this.intervalId_);
         this.intervalId_ = null;
       } else {
         nodeList = unreadyNodes;
       }
     }.bind(this), 10);
   },
 
   /**
    * Event wrapper for updateScroll_.
    * @param {!Event} event
    * @private
    */
   updateScrollEvent_: function(event) {
-    let scrollable = /** @type {!HTMLElement} */ (event.target);
+    var scrollable = /** @type {!HTMLElement} */ (event.target);
     this.updateScroll_(scrollable);
   },
 
   /**
    * This gets called once intially and any time a scrollable container scrolls.
    * @param {!HTMLElement} scrollable
    * @private
    */
   updateScroll_: function(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);
   },
 };