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

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

Index: chrome/test/data/webui/settings/ensure_lazy_loaded.js
diff --git a/chrome/test/data/webui/settings/ensure_lazy_loaded.js b/chrome/test/data/webui/settings/ensure_lazy_loaded.js
new file mode 100644
index 0000000000000000000000000000000000000000..f2bae8c03ed6ff965b0be66893ac91a5b00bf342
--- /dev/null
+++ b/chrome/test/data/webui/settings/ensure_lazy_loaded.js
@@ -0,0 +1,21 @@
+// Copyright 2017 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.
+
+cr.define('settings', function() {
+
+  function ensureLazyLoaded() {
+    // Only trigger lazy loading, if we are in top-level Settings page.
+    if (window.location.href == 'chrome://md-settings/') {
+      suiteSetup(function() {
+        return new Promise(function(resolve, reject) {
+          Polymer.Base.importHref('/lazy_load.html', resolve, reject, true);
+        });
+      });
+    }
+  }
+
+  return {
+    ensureLazyLoaded: ensureLazyLoaded,
+  };
+});