MD Settings: Lazy load the contents of the "advanced" settings.

chrome/test/data/webui/settings/settings_page_browsertest.js

 // Copyright 2015 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 Prototype for Settings page tests. */
 
 /** @const {string} Path to root from chrome/test/data/webui/settings/. */
 var ROOT_PATH = '../../../../../';
 
 // Polymer BrowserTest fixture.
@@ skipping 14 matching lines @@
 
   /** @override */
   extraLibraries: PolymerTest.getLibraries(ROOT_PATH).concat([
     '../fake_chrome_event.js',
     'fake_settings_private.js',
   ]),
 
   /** @override */
   runAccessibilityChecks: false,
 
+  /** @type {?SettingsBasicPageElement} */
+  page: null,
+
   /** @override */
   setUp: function() {
     PolymerTest.prototype.setUp.call(this);
     suiteSetup(function() {
       return CrSettingsPrefs.initialized;
     });
+
+    suiteSetup(function() {
+      return this.getPage('basic').then(function(basicPage) {
+        this.page = basicPage;
+      }.bind(this));
+    }.bind(this));
   },
 
   /**
    * Toggles the Advanced sections.
    */
   toggleAdvanced: function() {
     var settingsMain = document.querySelector('* /deep/ settings-main');
     assert(!!settingsMain);
     settingsMain.advancedToggleExpanded = !settingsMain.advancedToggleExpanded;
     Polymer.dom.flush();
   },
 
   /**
    * @param {string} type The settings page type, e.g. 'about' or 'basic'.
    * @return {!PolymerElement} The PolymerElement for the page.

[Dan Beam, 2017/03/16 20:52:22]

!Promise<!PolymerElement>

    */
   getPage: function(type) {
     var settingsUi = document.querySelector('settings-ui');
     assertTrue(!!settingsUi);
     var settingsMain = settingsUi.$$('settings-main');
     assertTrue(!!settingsMain);
     var pageType = 'settings-' + type + '-page';
     var page = settingsMain.$$(pageType);
     assertTrue(!!page);
-    var idleRender = page.$$('template[is=settings-idle-render]');
-    if (idleRender) {
-      idleRender.get();
-      Polymer.dom.flush();
-    }
-    return page;
+
+    var idleRender = page.$$('template[is=settings-idle-load]');
+    if (!idleRender)
+      return Promise.resolve(page);
+
+    return idleRender.get().then(function() {
+      return page;
+    });
   },
 
   /**
    * @param {!PolymerElement} page The PolymerElement for the page containing
    *     |section|.
    * @param {string} section The settings page section, e.g. 'appearance'.
    * @return {Node|undefined} The DOM node for the section.
    */
   getSection: function(page, section) {
     var sections = page.shadowRoot.querySelectorAll('settings-section');
@@ skipping 33 matching lines @@
     // Any other stamped subpages should not be visible.
     var subpages = stampedChildren.filter(function(element) {
       return element.getAttribute('route-path') != 'default';
     });
     for (var subpage of subpages) {
       assertEquals(subpage.offsetHeight, 0, 'Expected subpage #' + subpage.id +
           ' in ' + section.section + ' not to be visible.');
     }
   },
 };