Export a private webstore API to call into the new inline sign-in flow.

chrome/browser/signin/signin_promo.h

Index: chrome/browser/signin/signin_promo.h
diff --git a/chrome/browser/signin/signin_promo.h b/chrome/browser/signin/signin_promo.h
index e6a34f98dde9c6296896aee29e10bcc784137c21..a28862c2fb7aa231e64195213ff3d1505017af40 100644
--- a/chrome/browser/signin/signin_promo.h
+++ b/chrome/browser/signin/signin_promo.h
@@ -61,6 +61,13 @@ GURL GetLandingURL(const char* option, int value);
 GURL GetPromoURL(Source source, bool auto_close);
 GURL GetPromoURL(Source source, bool auto_close, bool is_constrained);
 
+// As above, but also appends the |continue_url| as a parameter to the URL.
+// A |continue_url| may be set only when not using the web-based sign-in flow.
+GURL GetPromoURLWithContinueURL(Source source,
+                                bool auto_close,
+                                bool is_constrained,
+                                GURL continue_url);
+
 // Returns a sign in promo URL specifically for reauthenticating |account_id|.
 GURL GetReauthURL(Profile* profile, const std::string& account_id);