Add feature flag for the new WebUI Crostini Installer

Bug: 929571
Change-Id: Iebcb92fdf8b1c09035a2ff82368a50dcdf8a3a37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1694183
Commit-Queue: Jason Lin <[email protected]>
Commit-Queue: Nicholas Verne <[email protected]>
Auto-Submit: Jason Lin <[email protected]>
Reviewed-by: Nicholas Verne <[email protected]>
Cr-Commit-Position: refs/heads/master@{#675924}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 8441f905..d983668 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1791,6 +1791,9 @@
 extern const char kCrostiniUsbSupportName[];
 extern const char kCrostiniUsbSupportDescription[];
 
+extern const char kCrostiniWebUIInstallerName[];
+extern const char kCrostiniWebUIInstallerDescription[];
+
 extern const char kCrosVmCupsProxyName[];
 extern const char kCrosVmCupsProxyDescription[];