[MD Bookmarks] Add Select for Bookmarks.

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 51 matching lines @@
     id: id,
     title: '',
     url: 'http://www.google.com/',
   };
   if (config) {
     for (var key in config)
       newItem[key] = config[key];
   }
   return newItem;
 }
+
+/**
+ * Sends a custom click event to |element|.
+ * @param {HTMLElement} element
+ * @param {Object} config
+ */
+function customClick(element, config) {

[calamity, 2017/01/17 06:12:22]

I would fill out config with a useful set of defaults just in case and then copy
things from the arg. See history's test_util.js:shiftClick for an example of
sane defaults.

[jiaxi, 2017/01/20 04:51:09]

Done.

+  element.dispatchEvent(new MouseEvent('mousedown', config));
+  element.dispatchEvent(new MouseEvent('mouseup', config));
+  element.dispatchEvent(new MouseEvent('click', config));
+}