[MD Bookmarks] Persist collapsed folders between page loads.

chrome/test/data/webui/md_bookmarks/md_bookmarks_browsertest.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.
 
 /**
  * @fileoverview Test suite for the Material Design bookmarks page.
  */
 var ROOT_PATH = '../../../../../';
 
 GEN_INCLUDE(
     [ROOT_PATH + 'chrome/test/data/webui/polymer_browser_test_base.js']);
 GEN('#include "base/command_line.h"');
 
 function MaterialBookmarksBrowserTest() {}
 
 MaterialBookmarksBrowserTest.prototype = {
   __proto__: PolymerTest.prototype,
 
   browsePreload: 'chrome://bookmarks',
 
   commandLineSwitches: [{switchName: 'enable-features',
                          switchValue: 'MaterialDesignBookmarks'}],
 
   extraLibraries: PolymerTest.getLibraries(ROOT_PATH).concat([
     'test_store.js',
     'test_util.js',
   ]),
 };
 
+function MaterialBookmarksAppTest() {}
+
+MaterialBookmarksAppTest.prototype = {
+  __proto__: MaterialBookmarksBrowserTest.prototype,
+
+  extraLibraries: MaterialBookmarksBrowserTest.prototype.extraLibraries.concat([
+    'app_test.js',
+  ]),
+};
+
+TEST_F('MaterialBookmarksAppTest', 'All', function() {
+  mocha.run();
+});
+
 function MaterialBookmarksDNDManagerTest() {}
 
 MaterialBookmarksDNDManagerTest.prototype = {
   __proto__: MaterialBookmarksBrowserTest.prototype,
 
   extraLibraries: MaterialBookmarksBrowserTest.prototype.extraLibraries.concat([
     'dnd_manager_test.js',
   ]),
 };
 
@@ skipping 109 matching lines @@
   __proto__: MaterialBookmarksBrowserTest.prototype,
 
   extraLibraries: MaterialBookmarksBrowserTest.prototype.extraLibraries.concat([
     'store_client_test.js',
   ]),
 };
 
 TEST_F('MaterialBookmarksStoreClientTest', 'All', function() {
   mocha.run();
 });