MD Settings: Deflake attempt for CrSettingsPrivacyPageTest.PrivacyPage.

chrome/test/data/webui/settings/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.
+
+cr.define('test_util', function() {
+  /**
+   * Observes an HTML attribute and fires a promise when it matches a given
+   * value.
+   * @param {!HTMLElement} target
+   * @param {string} attributeName
+   * @param {*} attributeValue
+   * @return {!Promise}
+   */
+  function whenAttributeIs(target, attributeName, attributeValue) {
+    function isDone() { return target[attributeName] === attributeValue; }
+
+    return isDone() ? Promise.resolve() : new Promise(function(resolve) {
+      new MutationObserver(function(mutations, observer) {
+        for (var mutation of mutations) {
+          assertEquals('attributes', mutation.type);
+          if (mutation.attributeName == attributeName && isDone()) {
+            observer.disconnect();
+            resolve();
+            return;
+          }
+        }
+      }).observe(
+          target, {attributes: true, childList: false, characterData: false});
+    });
+  }
+
+  /**
+   * Converts an event occurrence to a promise.
+   * @param {string} eventType
+   * @param {!HTMLElement} target
+   * @return {!Promise} A promise firing once the event occurs.
+   */
+  function eventToPromise(eventType, target) {
+    return new Promise(function(resolve, reject) {
+      target.addEventListener(eventType, resolve);
+    });
+  }
+
+  return {
+    eventToPromise: eventToPromise,
+    whenAttributeIs: whenAttributeIs,
+  };
+});