MD Bookmarks: Restore any previously selected folder when clearing search

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 286 matching lines @@
     // Work upwards through the tree from child.
     while (currentId) {
       if (currentId == ancestorId)
         return true;
       currentId = nodes[currentId].parentId;
     }
     return false;
   };
 
   /**
-   * @param {?string} selectedFolder
+   * @param {string} selectedFolder
    * @param {Action} action
    * @param {NodeList} nodes
-   * @return {?string}
+   * @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;
-      case 'finish-search':
-        return null;
-      case 'clear-search':
-        // TODO(tsergeant): Return to the folder that was selected before the
-        // search.
-        return nodes[ROOT_NODE_ID].children[0];
       case 'remove-bookmark':
         // When deleting the selected folder (or its ancestor), select the
         // parent of the deleted node.
         if (selectedFolder &&
             SelectedFolderState.isAncestorOf(nodes, action.id, selectedFolder))
           return assert(nodes[action.id].parentId);
         return selectedFolder;
       default:
         return selectedFolder;
     }
@@ skipping 86 matching lines @@
 
   return {
     reduceAction: reduceAction,
     ClosedFolderState: ClosedFolderState,
     NodeState: NodeState,
     SearchState: SearchState,
     SelectedFolderState: SelectedFolderState,
     SelectionState: SelectionState,
   };
 });