[MD Bookmarks] Add a drag and drop indicator to bookmarks.

chrome/browser/resources/md_bookmarks/util.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 Utility functions for the Bookmarks page.
  */
 
 cr.define('bookmarks.util', function() {
   /**
    * @param {!BookmarksPageState} state
    * @return {!Array<string>}
    */
   function getDisplayedList(state) {
-    if (state.selectedFolder)
-      return assert(state.nodes[state.selectedFolder].children);
+    if (!isShowingSearch(state))
+      return assert(state.nodes[assert(state.selectedFolder)].children);
 
     return state.search.results;
   }
 
   /**
    * @param {BookmarkTreeNode} rootNode
    * @return {NodeList}
    */
   function normalizeNodes(rootNode) {
     /** @type {NodeList} */
@@ skipping 33 matching lines @@
         inProgress: false,
         results: [],
       },
       selection: {
         items: {},
         anchor: null,
       },
     };
   }
 
+  /**
+   * @param {BookmarksPageState} state
+   * @return boolean
+   */
+  function isShowingSearch(state) {
+    return !state.selectedFolder;
+  }
+
+  /**
+   * @param {string} id
+   * @param {NodeList} nodes
+   * @return {boolean}
+   */
+  function hasChildFolders(id, nodes) {
+    var children = nodes[id].children;
+    for (var i = 0; i < children.length; i++) {
+      if (nodes[children[i]].children)
+        return true;
+    }
+    return false;
+  }
+
   return {
     createEmptyState: createEmptyState,
     getDisplayedList: getDisplayedList,
+    hasChildFolders: hasChildFolders,
+    isShowingSearch: isShowingSearch,
     normalizeNodes: normalizeNodes,
+    ROOT_NODE_ID: '0',
   };
 });