Options: Disable dragging when the list is disabled.

chrome/browser/resources/options/browser_options_startup_page_list.js

 // Copyright (c) 2011 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('options.browser_options', function() {
   const AutocompleteList = options.AutocompleteList;
   const InlineEditableItem = options.InlineEditableItem;
   const InlineEditableItemList = options.InlineEditableItemList;
 
   /**
@@ skipping 65 matching lines @@
 
       this.addEventListener('commitedit', this.onEditCommitted_);
 
       var self = this;
       urlField.addEventListener('focus', function(event) {
         self.parentNode.autocompleteList.attachToInput(urlField);
       });
       urlField.addEventListener('blur', function(event) {
         self.parentNode.autocompleteList.detach();
       });
+
       this.draggable = true;
     },
 
     /** @inheritDoc */
     get currentInputIsValid() {
       return this.urlField_.validity.valid;
     },
 
     /** @inheritDoc */
     get hasBeenEdited() {
@@ skipping 68 matching lines @@
       }
       return target;
     },
 
     /*
      * Handles the dragstart event.
      * @param {Event} e The dragstart event.
      * @private
      */
     handleDragStart_: function(e) {
+      // Prevent dragging if the list is disabled.
+      if (this.disabled) {
+        e.preventDefault();
+        return false;
+      }
+
       var target = e.target;
       // StartupPageListItem should be the only draggable element type in the
       // page but let's make sure.
       if (target instanceof StartupPageListItem) {
         this.draggedItem = target;
         this.draggedItem.editable = false;
         e.dataTransfer.effectAllowed = 'move';
         // We need to put some kind of data in the drag or it will be
         // ignored.  Use the URL in case the user drags to a text field or the
         // desktop.
@@ skipping 109 matching lines @@
       this.hideDropMarkerTimer_ = window.setTimeout(function() {
         $('startupPagesListDropmarker').style.display = '';
       }, 100);
     },
   };
 
   return {
     StartupPageList: StartupPageList
   };
 });