MD Downloads: fix up some Polymer 1.2.3 issues and re-vulcanize

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_: {
         type: Boolean,
         value: false,
       },
 
       items_: {
         type: Array,
       },
     },
 
+    hostAttributes: {
+      loading: true,
+    },
+
     /**
      * @param {Event} e
      * @private
      */
     onCanExecute_: function(e) {
       e = /** @type {cr.ui.CanExecuteEvent} */(e);
       switch (e.command.id) {
         case 'undo-command':
           e.canExecute = this.$.toolbar.canUndo();
           break;
@@ skipping 62 matching lines @@
         var isSearching = downloads.ActionService.getInstance().isSearching();
         var messageToShow = isSearching ? 'noSearchResults' : 'noDownloads';
         this.$['no-downloads'].querySelector('span').textContent =
             loadTimeData.getString(messageToShow);
       }
       this.hasDownloads_ = hasDownloads;
 
       if (loadTimeData.getBoolean('allowDeletingHistory'))
         this.$.toolbar.downloadsShowing = this.hasDownloads_;
 
-      this.$.panel.classList.remove('loading');
+      this.removeAttribute('loading');
     },
 
     /**
      * @param {!downloads.Data} data
      * @private
      */
     updateItem_: function(data) {
       var index = this.idToIndex_[data.id];
       this.set('items_.' + index, data);
       this.$['downloads-list'].updateSizeForItem(index);
@@ skipping 11 matching lines @@
   Manager.updateItem = function(item) {
     document.querySelector('downloads-manager').updateItem_(item);
   };
 
   Manager.onLoad = function() {
     document.querySelector('downloads-manager').onLoad_();
   };
 
   return {Manager: Manager};
 });