crostini: use test_util eventToPromise

Bug: None
Change-Id: I609cd25dbb3cf611dcd0f0a4c2d65e8e0ef50f43
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2083974
Commit-Queue: Julian Watson <juwa@google.com>
Commit-Queue: Nic Hollingum <hollingum@google.com>
Auto-Submit: Julian Watson <juwa@google.com>
Reviewed-by: Nic Hollingum <hollingum@google.com>
Cr-Commit-Position: refs/heads/master@{#746226}

chrome/test/data/webui/settings/chromeos/crostini_page_test.js

@@ -94,19 +94,6 @@ suite('CrostiniPageTests', function() {
     /** @type {?SettingsCrostiniSubPageElement} */
     let subpage;
 
-    /**
-     * Returns a new promise that resolves after a window 'popstate' event.
-     * @return {!Promise}
-     */
-    function whenPopState() {
-      return new Promise(function(resolve) {
-        window.addEventListener('popstate', function callback() {
-          window.removeEventListener('popstate', callback);
-          resolve();
-        });
-      });
-    }
-
     setup(function() {
       setCrostiniPrefs(true);
       loadTimeData.overrideValues({
@@ -398,7 +385,7 @@ suite('CrostiniPageTests', function() {
       assertEquals(
           1, crostiniBrowserProxy.getCallCount('requestRemoveCrostini'));
       setCrostiniPrefs(false);
-      return whenPopState().then(function() {
+      return test_util.eventToPromise('popstate', window).then(function() {
         assertEquals(
             settings.Router.getInstance().getCurrentRoute(),
             settings.routes.CROSTINI);
@@ -433,7 +420,7 @@ suite('CrostiniPageTests', function() {
           settings.Router.getInstance().getCurrentRoute(),
           settings.routes.CROSTINI_DETAILS);
       setCrostiniPrefs(false);
-      return whenPopState().then(function() {
+      return test_util.eventToPromise('popstate', window).then(function() {
         assertEquals(
             settings.Router.getInstance().getCurrentRoute(),
             settings.routes.CROSTINI);

chrome/test/data/webui/settings/chromeos/os_settings_browsertest.js

@@ -447,6 +447,7 @@ var OSSettingsCrostiniPageTest = class extends OSSettingsBrowserTest {
   get extraLibraries() {
     return super.extraLibraries.concat([
       '//ui/webui/resources/js/promise_resolver.js',
+      BROWSER_SETTINGS_PATH + '../test_util.js',
       BROWSER_SETTINGS_PATH + '../test_browser_proxy.js',
       'test_crostini_browser_proxy.js',
       'crostini_page_test.js',