Add flag for HTTP Auth committed interstitials.

This CL adds a flag and feature for enabling HTTP auth via committed
interstitials. Nothing uses it yet.

Change-Id: Ia7d2e3b0c66b22cfd5fa56c6ec65f2289a2665d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1589013
Commit-Queue: Joe DeBlasio <[email protected]>
Auto-Submit: Joe DeBlasio <[email protected]>
Reviewed-by: Emily Stark <[email protected]>
Cr-Commit-Position: refs/heads/master@{#655106}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index e9cd8d9..8d08faa 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -1112,6 +1112,12 @@
 const char kHostedAppShimCreationDescription[] =
     "Create app shims on Mac when creating a hosted app.";
 
+const char kHTTPAuthCommittedInterstitialsName[] =
+    "Enable Committed Interstitials for HTTP Auth";
+const char kHTTPAuthCommittedInterstitialsDescription[] =
+    "Use committed error pages instead of transient navigation entries "
+    "for HTTP auth interstitial pages.";
+
 const char kIconNtpName[] = "Large icons on the New Tab page";
 const char kIconNtpDescription[] =
     "Enable the experimental New Tab page using large icons.";