Add enable-desktop-pwas-local-updating flag

This CL adds a feature flag in preparation for implementing local PWA
updates when changes to site manifest data are detected.

Bug: 926083
Change-Id: I8f1f79cf8492933b9b7b6b703384da3f38eaeb32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1697662
Commit-Queue: Alan Cutter <[email protected]>
Auto-Submit: Alan Cutter <[email protected]>
Reviewed-by: Raymes Khoury <[email protected]>
Cr-Commit-Position: refs/heads/master@{#676759}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index cb4ad20..5d9db58 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -358,6 +358,9 @@
 extern const char kEnableDesktopPWAsName[];
 extern const char kEnableDesktopPWAsDescription[];
 
+extern const char kDesktopPWAsLocalUpdatingName[];
+extern const char kDesktopPWAsLocalUpdatingDescription[];
+
 extern const char kDesktopPWAsOmniboxInstallName[];
 extern const char kDesktopPWAsOmniboxInstallDescription[];