[MD Bookmarks] Persist collapsed folders between page loads.

chrome/browser/ui/webui/md_bookmarks/md_bookmarks_ui.cc

 // Copyright (c) 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.
 
 #include "chrome/browser/ui/webui/md_bookmarks/md_bookmarks_ui.h"
 
 #include <algorithm>
 
 #include "base/strings/string16.h"
 #include "chrome/browser/profiles/profile.h"
@@ skipping 57 matching lines @@
   AddLocalizedString(source, "title", IDS_MD_BOOKMARK_MANAGER_TITLE);
 
   // Resources.
   source->AddResourcePath("actions.html", IDR_MD_BOOKMARKS_ACTIONS_HTML);
   source->AddResourcePath("actions.js", IDR_MD_BOOKMARKS_ACTIONS_JS);
   source->AddResourcePath("api_listener.html",
                           IDR_MD_BOOKMARKS_API_LISTENER_HTML);
   source->AddResourcePath("api_listener.js", IDR_MD_BOOKMARKS_API_LISTENER_JS);
   source->AddResourcePath("app.html", IDR_MD_BOOKMARKS_APP_HTML);
   source->AddResourcePath("app.js", IDR_MD_BOOKMARKS_APP_JS);
+  source->AddResourcePath("constants.html", IDR_MD_BOOKMARKS_CONSTANTS_HTML);
+  source->AddResourcePath("constants.js", IDR_MD_BOOKMARKS_CONSTANTS_JS);
   source->AddResourcePath("dnd_manager.html",
                           IDR_MD_BOOKMARKS_DND_MANAGER_HTML);
   source->AddResourcePath("dnd_manager.js", IDR_MD_BOOKMARKS_DND_MANAGER_JS);
   source->AddResourcePath("edit_dialog.html",
                           IDR_MD_BOOKMARKS_EDIT_DIALOG_HTML);
   source->AddResourcePath("edit_dialog.js", IDR_MD_BOOKMARKS_EDIT_DIALOG_JS);
   source->AddResourcePath("folder_node.html",
                           IDR_MD_BOOKMARKS_FOLDER_NODE_HTML);
   source->AddResourcePath("folder_node.js",
                           IDR_MD_BOOKMARKS_FOLDER_NODE_JS);
@@ skipping 33 matching lines @@
   // Set up the chrome://bookmarks/ source.
   Profile* profile = Profile::FromWebUI(web_ui);
   content::WebUIDataSource::Add(profile,
                                 CreateMdBookmarksUIHTMLSource(profile));
 }
 
 // static
 bool MdBookmarksUI::IsEnabled() {
   return base::FeatureList::IsEnabled(features::kMaterialDesignBookmarks);
 }