MD Bookmarks: Prevent flash of folder contents when changing search term

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 100 matching lines @@
 
   /**
    * @param {SearchState} search
    * @param {Action} action
    * @return {SearchState}
    */
   SearchState.startSearch = function(search, action) {
     return {
       term: action.term,
       inProgress: true,
-      results: [],
+      results: search.results,
     };
   };
 
   /**
    * @param {SearchState} search
    * @param {Action} action
    * @return {SearchState}
    */
   SearchState.finishSearch = function(search, action) {
     return /** @type {SearchState} */ (Object.assign({}, search, {
       inProgress: false,
       results: action.results,
     }));
   };
 
   /** @return {SearchState} */
   SearchState.clearSearch = function() {
     return {
       term: '',
       inProgress: false,
-      results: [],
+      results: null,
     };
   };
 
   /**
    * @param {SearchState} search
    * @param {!Set<string>} deletedIds
    * @return {SearchState}
    */
   SearchState.removeDeletedResults = function(search, deletedIds) {
+    if (!search.results)
+      return search;
+
     var newResults = [];
     search.results.forEach(function(id) {
       if (!deletedIds.has(id))
         newResults.push(id);
     });
     return /** @type {SearchState} */ (Object.assign({}, search, {
       results: newResults,
     }));
   };
 
@@ skipping 314 matching lines @@
   return {
     reduceAction: reduceAction,
     ClosedFolderState: ClosedFolderState,
     NodeState: NodeState,
     PreferencesState: PreferencesState,
     SearchState: SearchState,
     SelectedFolderState: SelectedFolderState,
     SelectionState: SelectionState,
   };
 });