Use svg icon to avoid lazy loading of Polymer elements for user pods

ui/login/account_picker/user_pod_template.js

-// Copyright (c) 2016 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.
-
-(function() {
-  "use strict";
-
-  var RESOURCES_TO_LOAD = [
-    'chrome://resources/polymer/v1_0/iron-icons/iron-icons.html',
-    'chrome://resources/polymer/v1_0/paper-button/paper-button.html'
-  ];
-  /* const */ var IDLE_TIMEOUT_MS = 200;
-
-  window.addEventListener('load', function() {
-    // The user pod template gets cloned shortly after the load event to make
-    // the actual user pods. It then takes a few update cycles to style these
-    // elements. Loading polymer will block the DOM, so we try to load polymer
-    // after the user pods have been cloned and styled.
-    requestIdleCallback(function() {
-      for (var resourceUrl of RESOURCES_TO_LOAD) {
-        var link = document.createElement('link');
-        link.rel = 'import';
-        link.href = resourceUrl;
-        document.head.appendChild(link);
-      }
-    }, { timeout: IDLE_TIMEOUT_MS });
-  });
-})();