Add a sign-in promo message to the Other Devices menu.

chrome/browser/resources/ntp4/new_tab.css

Index: chrome/browser/resources/ntp4/new_tab.css
diff --git a/chrome/browser/resources/ntp4/new_tab.css b/chrome/browser/resources/ntp4/new_tab.css
index de5e6fc089e2516807012367f681bf99d4eea653..088304138a50aa7598b97f50118506e364dc67f6 100644
--- a/chrome/browser/resources/ntp4/new_tab.css
+++ b/chrome/browser/resources/ntp4/new_tab.css
@@ -423,3 +423,16 @@ html[dir='rtl'] #chrome-web-store-title {
 #other-sessions-menu-button.invisible {
   display: none;
 }
+
+.other-sessions-promo-message {
+  display: none;
+  padding: 0;
+}
+
+.other-sessions-promo-message:only-child {
+  display: block;
+}
+
+.other-sessions-promo-message p {
+  margin: 0;
+}