MD Settings: Lazy-load sub-pages.

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 57 matching lines @@
   getSection: function(page, section) {
     var sections = page.shadowRoot.querySelectorAll('settings-section');
     assertTrue(!!sections);
     for (var i = 0; i < sections.length; ++i) {
       var s = sections[i];
       if (s.section == section)
         return s;
     }
     return undefined;
   },
+
+  /**
+   * Verifies the section has a visible #main element and that any possible
+   * sub-pages are hidden.
+   * @param {!Node} The DOM node for the section.
+   */
+  verifySubpagesHidden: function(section) {
+    // Check if there are sub-pages to verify.
+    var pages = section.querySelector('* /deep/ settings-animated-pages');
+    if (!pages)
+      return;
+
+    var children = pages.getContentChildren();
+    var stampedChildren = children.filter(function(element) {
+      return element.tagName != 'TEMPLATE';
+    });
+
+    // The section's main child should be stamped and visible.
+    var main = stampedChildren.filter(function(element) {
+      return element.id == 'main';
+    });
+    assertEquals(main.length, 1, '#main not found for section ' +
+        section.section);
+    assertGT(main[0].offsetHeight, 0);
+
+    // Any other stamped subpages should not be visible.
+    var subpages = stampedChildren.filter(function(element) {
+      return element.id != 'main';
+    });
+    for (var subpage of subpages) {
+      assertEquals(subpage.offsetHeight, 0, 'Expected subpage #' + subpage.id +
+          ' in ' + section.section + ' not to be visible.');
+    }
+  },
 };