MD Settings: Prevent direct navigation to disabled Site Settings UI.

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

Index: chrome/test/data/webui/settings/cr_settings_browsertest.js
diff --git a/chrome/test/data/webui/settings/cr_settings_browsertest.js b/chrome/test/data/webui/settings/cr_settings_browsertest.js
index 565e21258953a40bc45e1a3645357c7627595aaf..9bb396ae1b435c7e091df1e41777caaa67ffff45 100644
--- a/chrome/test/data/webui/settings/cr_settings_browsertest.js
+++ b/chrome/test/data/webui/settings/cr_settings_browsertest.js
@@ -759,6 +759,11 @@ CrSettingsSiteSettingsTest.prototype = {
   browsePreload: 'chrome://md-settings/privacy_page/privacy_page.html',
 
   /** @override */
+  commandLineSwitches: [{
+    switchName: 'enable-site-settings',
+  }],
+
+  /** @override */
   extraLibraries: CrSettingsBrowserTest.prototype.extraLibraries.concat([
     // TODO(dbeam): split these up.
     'category_default_setting_tests.js',