Update the 'managed user import' overlay to show an avatar selection grid

chrome/browser/resources/options/managed_user_import.css

 /* Copyright 2013 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. */
 
 #create-new-user-link {
   position: absolute;
 }
 
 #managed-user-import {
-  height: 400px;
   width: 612px;
 }
 
 #managed-user-import-text {
   padding-bottom: 10px;
   padding-left: 17px;
   white-space: pre-wrap;
   word-wrap: break-word;
 }
 
+#managed-user-list {
+  height: 240px;
+}
+
+#select-avatar-grid {
+  background-color: rgba(255, 255, 255, 0.75);
+  padding: 2px;
+}
+
 #managed-user-import-error-bubble {
   -webkit-transition: max-height 200ms, padding 200ms;
   background-color: rgb(238, 185, 57);
   border-radius: 4px;
   font-weight: bold;
   margin-left: auto;
   margin-right: auto;
   margin-top: 10px;
   max-height: 50px;
   overflow: hidden;
@@ skipping 11 matching lines @@
 }
 
 .profile-name-disabled {
   color: rgb(153, 153, 153);
 }
 
 .already-on-this-device {
   padding-left: 4px;
   padding-right: 4px;
 }