Add ServiceWorkerImportedScriptUpdateCheck flag

This CL tentatively adds ServiceWorkerImportedScriptUpdateCheck flag.
It is for the implementation of byte-for-byte update check for
service worker importScripts() resources. We are going to implement
the feature under this flag and flip it over once it is completed.

Bug: 648295
Change-Id: Iabb6140af84382ecd0d07ee28283490c303e8c4d
Reviewed-on: https://chromium-review.googlesource.com/1192571
Commit-Queue: Momoko Hattori <[email protected]>
Reviewed-by: Kinuko Yasuda <[email protected]>
Reviewed-by: Makoto Shimazu <[email protected]>
Cr-Commit-Position: refs/heads/master@{#587017}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 07ff311c..6c3563f 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -1616,6 +1616,12 @@
 const char kServiceWorkerPaymentAppsDescription[] =
     "Enable Service Worker applications to integrate as payment apps";
 
+const char kServiceWorkerImportedScriptUpdateCheckName[] =
+    "Enable update check for service worker importScripts() resources";
+const char kServiceWorkerImportedScriptUpdateCheckDescription[] =
+    "Extend byte-for-byte update check for scripts that are imported by the "
+    "service worker script via importScripts().";
+
 extern const char kServiceWorkerServicificationName[] =
     "Servicified service workers";
 extern const char kServiceWorkerServicificationDescription[] =