[MD Bookmarks] Change selection items from Map to Set.

chrome/test/data/webui/md_bookmarks/test_util.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.
 
 /**
  * Replace the current body of the test with a new element.
  * @param {Element} element
  */
 function replaceBody(element) {
   PolymerTest.clearBody();
@@ skipping 65 matching lines @@
     url: 'http://www.google.com/',
   };
   if (config) {
     for (var key in config)
       newItem[key] = config[key];
   }
   return newItem;
 }
 
 /**
+ * @param {Set<T>}
+ * @return {Array<T>}
+ * @template T
+ */
+function normalizeSet(set) {
+  return Array.from(set).sort();
+}
+
+/**
  * Sends a custom click event to |element|.
  * @param {HTMLElement} element
  * @param {Object=} config
  */
 function customClick(element, config) {
   var props = {
     bubbles: true,
     cancelable: true,
     buttons: 1,
     shiftKey: false,
     ctrlKey: false,
   };
 
   if (config) {
     for (var key in config)
       props[key] = config[key];
   }
 
   element.dispatchEvent(new MouseEvent('mousedown', props));
   element.dispatchEvent(new MouseEvent('mouseup', props));
   element.dispatchEvent(new MouseEvent('click', props));
 }