Add a blocking version of the sync promo dialog

chrome/browser/resources/sync_promo/sync_promo.css

 /* Copyright (c) 2012 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.
  */
 
 html {
   font-family: segoe ui, arial, helvetica, sans-serif;
   font-size: 13px;
 }
 
 html, body {
   margin: 0;
   min-height: 100%;
   min-width: 100%;
   padding 0;
   position: absolute;
 }
 
+body {
+  -webkit-transition: all 0.2s;
+  opacity: 0;
+}
+
+body.loaded {
+  opacity: 1;
+}
+
 html[promo-version='0'] body {
   background-image: -webkit-linear-gradient(
       rgba(0, 0, 0, 0.0), rgba(0, 0, 0, 0.04));
 }
 
 #sync-setup-overlay {
   background-color: transparent;
   margin: 0;
   width: 100%;
 }
@@ skipping 81 matching lines @@
 }
 
 #promo-skip-button {
   -webkit-margin-end: 25px;
 }
 
 /* Page Title. ****************************************************************/
 
 #promo-title-container {
   display: block;
-  margin-bottom: 35px;
-  margin-top: 37px;
+  margin: 37px 44px 35px;
   text-align: center;
 }
 
-html[promo-version='1'] #promo-title-container,
-html[promo-version='3'] #promo-title-container {
-  margin-top: 41px;
-}
-
 html[promo-version='2'] #promo-title-container {
   display: none;
 }
 
 h1 {
   color: rgb(34, 34, 34);
   font-size: 27px;
   font-weight: normal;
   margin: 0;
 }
@@ skipping 166 matching lines @@
 
 html[promo-version='0'] #sync-setup-login-promo-column-0,
 html[promo-version='1'] #sync-setup-login-promo-column-1,
 html[promo-version='2'] #sync-setup-login-promo-column-2 {
   display: block;
 }
 
 #sync-setup-login-promo-column {
   -webkit-margin-end: 385px;
 }