Add chrome://site-engagement WebUI.

chrome/browser/resources/engagement/site_engagement.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.
+
+'use strict';
+
+define('main', [
+    'mojo/public/js/connection',
+    'chrome/browser/ui/webui/engagement/site_engagement.mojom',
+    'content/public/renderer/service_provider',
+], function(connection, siteEngagementMojom, serviceProvider) {
+
+  return function() {
+    var uiHandler = connection.bindHandleToProxy(
+        serviceProvider.connectToService(
+            siteEngagementMojom.SiteEngagementUIHandler.name),
+        siteEngagementMojom.SiteEngagementUIHandler);
+
+    // Populate engagement table.
+    uiHandler.getSiteEngagementInfo().then(response => {
+      $('engagement-table').engagementInfo = response.info;
+    });
+  };
+});