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

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

Index: chrome/test/data/webui/settings/settings_idle_render_browsertest.js
diff --git a/chrome/test/data/webui/settings/settings_idle_render_browsertest.js b/chrome/test/data/webui/settings/settings_idle_render_browsertest.js
index 8f3b42138e6c0d2db8aa4c3e0492b48e583710c5..ec7aba848bef49e1790bcc7beb261588cf12f169 100644
--- a/chrome/test/data/webui/settings/settings_idle_render_browsertest.js
+++ b/chrome/test/data/webui/settings/settings_idle_render_browsertest.js
@@ -37,7 +37,7 @@ TEST_F('SettingsIdleRenderBrowserTest', 'render', function() {
   suite('Settings idle render tests', function() {
     setup(function() {
       var template =
-          '<template is="settings-idle-render" id="idleTemplate">' +
+          '<template is="settings-idle-load" id="idleTemplate" url="">' +

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

is there anything real we could put here to simplify prod code to assume url
always exists?

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

Done. Found one that works.

           '  <div>' +
           '  </div>' +
           '</template>';
@@ -48,9 +48,11 @@ TEST_F('SettingsIdleRenderBrowserTest', 'render', function() {
 
     test('stamps after get()', function() {
       // Calling get() will force stamping without waiting for idle time.
-      var inner = document.getElementById('idleTemplate').get();
-      assertEquals('DIV', inner.nodeName);
-      assertEquals(inner, document.body.querySelector('div'));
+      return document.getElementById('idleTemplate').get().then(
+          function(inner) {
+            assertEquals('DIV', inner.nodeName);
+            assertEquals(inner, document.body.querySelector('div'));
+          });
     });
 
     test('stamps after idle', function(done) {