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

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

Index: chrome/test/data/webui/settings/help_page_browsertest.js
diff --git a/chrome/test/data/webui/settings/help_page_browsertest.js b/chrome/test/data/webui/settings/help_page_browsertest.js
index 2925dfbc0713948229630687dfdee2833658b31f..54c841706a786427830d3a446cc742a2efe2e969 100644
--- a/chrome/test/data/webui/settings/help_page_browsertest.js
+++ b/chrome/test/data/webui/settings/help_page_browsertest.js
@@ -24,6 +24,11 @@ SettingsHelpPageBrowserTest.prototype = {
 
   /** @override */
   extraLibraries: PolymerTest.getLibraries(ROOT_PATH),
+
+  /** @override */
+  setUp: function() {

[Dan Beam, 2017/03/17 00:30:05]

why can't we just make .basicPage null in tests?

then you could do:

return self.getPage('about').then(function(aboutPage) {
  expectFalse(self.basicPage);
  expectTrue(!!self.getSection(page, 'about');
});

[dpapad, 2017/03/17 20:53:55]

Not fully understanding the suggestion. Overriding setUp() achieves exactly
that, not initializing 'basicPage', since it does not really exist in the DOM,
when you visit chrome://help.

+    PolymerTest.prototype.setUp.call(this);
+  },
 };
 
 TEST_F('SettingsHelpPageBrowserTest', 'Load', function() {
@@ -34,8 +39,9 @@ TEST_F('SettingsHelpPageBrowserTest', 'Load', function() {
   // Register mocha tests.
   suite('Help page', function() {
     test('about section', function() {
-      var page = self.getPage('about');
-      expectTrue(!!self.getSection(page, 'about'));
+      return self.getPage('about').then(function(page) {
+        expectTrue(!!self.getSection(page, 'about'));
+      });
     });
   });