Create a field test for sync sign in promo strings.

chrome/browser/ui/webui/sync_promo_handler.h

Index: chrome/browser/ui/webui/sync_promo_handler.h
===================================================================
--- chrome/browser/ui/webui/sync_promo_handler.h	(revision 111699)
+++ chrome/browser/ui/webui/sync_promo_handler.h	(working copy)
@@ -25,6 +25,8 @@
   virtual void RegisterMessages() OVERRIDE;
 
   // SyncSetupFlowHandler implementation.
+  virtual void ShowGaiaSuccessAndClose() OVERRIDE;
+  virtual void ShowGaiaSuccessAndSettingUp() OVERRIDE;
   virtual void ShowConfigure(const base::DictionaryValue& args) OVERRIDE;
 
   // content::NotificationObserver implementation.
@@ -71,6 +73,9 @@
   // Record a user's flow through the promo to our histogram in UMA.
   void RecordUserFlowAction(int action);
 
+  // Load any experiments that run on the promo page.
+  void LoadPromoExperiments();
+
   // Use this to register for certain notifications (currently when tabs or
   // windows close).
   content::NotificationRegistrar registrar_;