Add a blocking version of the sync promo dialog

chrome/browser/resources/sync_promo/sync_promo.css

Index: chrome/browser/resources/sync_promo/sync_promo.css
diff --git a/chrome/browser/resources/sync_promo/sync_promo.css b/chrome/browser/resources/sync_promo/sync_promo.css
index 5c0e10247b095ba52e41aed8491146e39e6e0150..0489ef266f82610824f958fbb3773ff62c559a78 100644
--- a/chrome/browser/resources/sync_promo/sync_promo.css
+++ b/chrome/browser/resources/sync_promo/sync_promo.css
@@ -16,6 +16,15 @@ html, body {
   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));
@@ -117,16 +126,10 @@ html[promo-version='3'] #sync-setup-login-content-column {
 
 #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;
 }