Feature flag for Crostini Port Forwarding

Port forwarding is a new feature within crostini, users will be able to
access the feature setting through the crostini settings page. Whilst
it is being worked on, we should keep it behind a feature flag that is
disabled by default.

Bug: chromium/848127
Test: Make sure chromium builds, able to see the new flag in
chrome: //flags on the DUT
Change-Id: I36f66a8eecfc1cd169ec5f3c1d567c7147ca7007
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1988607
Commit-Queue: Matthew Chen <[email protected]>
Reviewed-by: David Munro <[email protected]>
Reviewed-by: Nic Hollingum <[email protected]>
Reviewed-by: Fergus Dall <[email protected]>
Cr-Commit-Position: refs/heads/master@{#729245}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 9362e79..a78fae2 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1981,6 +1981,9 @@
 extern const char kCrostiniBackupName[];
 extern const char kCrostiniBackupDescription[];
 
+extern const char kCrostiniPortForwardingName[];
+extern const char kCrostiniPortForwardingDescription[];
+
 extern const char kCrostiniUseBusterImageName[];
 extern const char kCrostiniUseBusterImageDescription[];