MD Downloads: handle date hiding/showing more sanely

chrome/browser/resources/md_downloads/manager.js

 // Copyright 2015 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.
 
 cr.define('downloads', function() {
   var Manager = Polymer({
     is: 'downloads-manager',
 
     properties: {
       hasDownloads_: {
@@ skipping 132 matching lines @@
      * @param {number} start
      * @param {number} end
      * @private
      */
     updateHideDates_: function(start, end) {
       for (var i = start; i <= end; ++i) {
         var current = this.items_[i];
         if (!current)
           continue;
         var prev = this.items_[i - 1];
-        current.hideDate = !!prev && prev.date_string == current.date_string;
+        var hideDate = !!prev && prev.date_string == current.date_string;
+        this.set('items_.' + i + '.hideDate', hideDate);
       }
     },
 
     /**
      * @param {number} index
      * @param {!downloads.Data} data
      * @private
      */
     updateItem_: function(index, data) {
       this.set('items_.' + index, data);
@@ skipping 24 matching lines @@
   Manager.removeItem = function(index) {
     Manager.get().removeItem_(index);
   };
 
   Manager.updateItem = function(index, data) {
     Manager.get().updateItem_(index, data);
   };
 
   return {Manager: Manager};
 });