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 3ec43b5603ff3be2b3ad85230f553f807e706a26..82a03de3523c5a32920b31d1f1f07ea26e4f1a70 100644
--- a/content/common/notification_type.h
+++ b/content/common/notification_type.h
@@ -1346,6 +1346,9 @@ 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.