[MD Bookmarks] Convert bookmark list to iron-list.

chrome/browser/resources/md_bookmarks/dnd_manager.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.
 
 cr.define('bookmarks', function() {
   /**
    * @param {BookmarkElement} element
    * @return {boolean}
    */
   function isBookmarkItem(element) {
@@ skipping 568 matching lines @@
 
       // Don't allow dropping below an expanded sidebar folder item since it is
       // confusing to the user anyway.
       if (isOverFolderNode && !state.closedFolders.has(overElement.itemId) &&
           bookmarks.util.hasChildFolders(overElement.itemId, state.nodes)) {
         return validDropPositions;
       }
 
       var nextElement = overElement.nextElementSibling;
 
-      // The template element sits past the end of the last bookmark element.
-      if (!isBookmarkItem(nextElement) && !isBookmarkFolderNode(nextElement))
-        nextElement = null;
-
       // Cannot drop below if the item below is already in the drag source.
       if (!nextElement || !dragInfo.isDraggingBookmark(nextElement.itemId))
         validDropPositions |= DropPosition.BELOW;
 
       return validDropPositions;
     },
 
     /**
      * Determine whether we can drop the dragged items on the drop target.
      * @private
@@ skipping 24 matching lines @@
       this.dropIndicator_.setTimeout = this.setTimeout_;
     }
   };
 
   return {
     DNDManager: DNDManager,
     DragInfo: DragInfo,
     DropIndicator: DropIndicator,
   };
 });