MD Bookmarks: Prevent navigating to invalid folders

chrome/browser/resources/md_bookmarks/reducers.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.
 
 /**
  * @fileoverview Module of functions which produce a new page state in response
  * to an action. Reducers (in the same sense as Array.prototype.reduce) must be
  * pure functions: they must not modify existing state objects, or make any API
  * calls.
  */
@@ skipping 295 matching lines @@
   /**
    * @param {string} selectedFolder
    * @param {Action} action
    * @param {NodeMap} nodes
    * @return {string}
    */
   SelectedFolderState.updateSelectedFolder = function(
       selectedFolder, action, nodes) {
     switch (action.name) {
       case 'select-folder':
-        // TODO(tsergeant): It should not be possible to select a non-folder.
         return action.id;
       case 'change-folder-open':
         // When hiding the selected folder by closing its ancestor, select
         // that ancestor instead.
         if (!action.open && selectedFolder &&
             SelectedFolderState.isAncestorOf(
                 nodes, action.id, selectedFolder)) {
           return action.id;
         }
         return selectedFolder;
@@ skipping 96 matching lines @@
 
   return {
     reduceAction: reduceAction,
     ClosedFolderState: ClosedFolderState,
     NodeState: NodeState,
     SearchState: SearchState,
     SelectedFolderState: SelectedFolderState,
     SelectionState: SelectionState,
   };
 });