Update the web store promo to be clearer and configurable at run-time.

content/common/notification_type.h

Index: content/common/notification_type.h
diff --git a/content/common/notification_type.h b/content/common/notification_type.h
index 8a0dff96802d3f882b26e02725ce4399003c8dfd..5e7b9c0718f08360c656439302fadb6d02d722bb 100644
--- a/content/common/notification_type.h
+++ b/content/common/notification_type.h
@@ -1322,6 +1322,9 @@ class NotificationType {
     // process/route id pair for the RenderViewHost. There are no details.
     PRERENDER_CONTENTS_USED,
 
+    // Sent when a new web store promo has been loaded.
+    WEB_STORE_PROMO_LOADED,
+
     // Count (must be last) ----------------------------------------------------
     // Used to determine the number of notification types.  Not valid as
     // a type parameter when registering for or posting notifications.