[Autofill] Implement Credit Card Signin Promo

A follow-up change will split the slightly long promo over 2-lines for Views, Mac, Android.

Also, Android and iOS will need bridges into Java and ObjC, so this is deferred to another change.

BUG=626442

Review-Url: https://codereview.chromium.org/2124343002
Cr-Commit-Position: refs/heads/master@{#404470}
diff --git a/components/autofill_strings.grdp b/components/autofill_strings.grdp
index 5dad21de..c90af58 100644
--- a/components/autofill_strings.grdp
+++ b/components/autofill_strings.grdp
@@ -20,6 +20,9 @@
   <message name="IDS_AUTOFILL_WARNING_INSECURE_CONNECTION" desc="Warning text to show when credit card autofill is disabled because the website is not using a secure connection.">
     Automatic credit card filling is disabled because this form does not use a secure connection.
   </message>
+  <message name="IDS_AUTOFILL_CREDIT_CARD_SIGNIN_PROMO" desc="Promo text shown alongside credit card suggestions to get people to sign in.">
+    Sign in to Chrome to use cards you saved to your Google Account.
+  </message>
   <if expr="_google_chrome">
     <message name="IDS_AUTOFILL_DELETE_AUTOCOMPLETE_SUGGESTION_CONFIRMATION_BODY" desc="Text in a dialog to confirm that the user wants to delete an autocomplete form history suggestion.">
       Remove form suggestion from Chrome?