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

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index a51057fd58a10efa7872a1484f1df9cbb6e2d9be..2abd497b11a136f1c471d8e1a0b56cc69ed3d7ba 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -9340,6 +9340,9 @@ experiment id: "<ph name="EXPERIMENT_ID">$5<ex>ar1</ex></ph>"
                desc="The message for the 'Other Sessions' menu on the New Tab Page, when there are no other sessions.">
         Access your open tabs on all of your devices.
       </message>
+      <message name="IDS_NEW_TAB_OTHER_SESSIONS_LEARN_MORE_URL" desc="URL of help center page explaining what the 'Other Sessions' menu is.">
+        http://support.google.com/chrome/bin/answer.py?answer=185277&amp;hl=[GRITLANGCODE]
+      </message>
       <if expr="pp_ifdef('android')">
         <message name="IDS_NEW_TAB_OTR_MESSAGE_MOBILE"
                  desc="Mobile: Used when a person opens an OTR tab">