Showing the promo on release channel only.

chrome/browser/chromeos/extensions/file_browser_private_api.cc

Index: chrome/browser/chromeos/extensions/file_browser_private_api.cc
diff --git a/chrome/browser/chromeos/extensions/file_browser_private_api.cc b/chrome/browser/chromeos/extensions/file_browser_private_api.cc
index 48fa84f8663fc9fbf5d0a525d22c09a991c8d49b..863faf84a306b7b1af8fcbc51b762628cffdcb0c 100644
--- a/chrome/browser/chromeos/extensions/file_browser_private_api.cc
+++ b/chrome/browser/chromeos/extensions/file_browser_private_api.cc
@@ -38,6 +38,7 @@
 #include "chrome/browser/ui/browser_window.h"
 #include "chrome/browser/ui/views/select_file_dialog_extension.h"
 #include "chrome/browser/ui/webui/extensions/extension_icon_source.h"
+#include "chrome/common/chrome_version_info.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/extension_icon_set.h"
 #include "chrome/common/extensions/file_browser_handler.h"
@@ -1728,6 +1729,9 @@ bool FileDialogStringsFunction::RunImpl() {
     board = "unknown";
   dict->SetString(kMachineInfoBoard, board);
 
+  dict->SetString("BROWSER_VERSION_MODIFIER",
+                  chrome::VersionInfo::GetVersionStringModifier());
+
   return true;
 }