MD Bookmarks: Fix Meta-down not triggering the 'Open' command on Mac

chrome/browser/resources/md_bookmarks/list.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.
 
 Polymer({
   is: 'bookmarks-list',
 
   behaviors: [
     bookmarks.StoreClient,
   ],
@@ skipping 141 matching lines @@
   onItemKeydown_: function(e) {
     var handled = true;
     var list = this.$.bookmarksCard;
     var focusMoved = false;
     var focusedIndex =
         this.getIndexForItemElement_(/** @type {HTMLElement} */ (e.target));
     var oldFocusedIndex = focusedIndex;
     if (e.key == 'ArrowUp') {
       focusedIndex--;
       focusMoved = true;
-    } else if (e.key == 'ArrowDown') {
+    } else if (e.key == 'ArrowDown' && !(cr.isMac && e.metaKey)) {
       focusedIndex++;
       focusMoved = true;
       e.preventDefault();
     } else if (e.key == 'Home') {
       focusedIndex = 0;
       focusMoved = true;
     } else if (e.key == 'End') {
       focusedIndex = list.items.length - 1;
       focusMoved = true;
     } else if (e.key == ' ' && e.ctrlKey) {
@@ skipping 40 matching lines @@
 
     if (!handled) {
       handled = bookmarks.CommandManager.getInstance().handleKeyEvent(
           e, this.getState().selection.items);
     }
 
     if (handled)
       e.stopPropagation();
   },
 });