Add NTLM single-sign-on support via Samba's ntlm_auth helper

net/http/http_auth_controller.cc

Index: net/http/http_auth_controller.cc
diff --git a/net/http/http_auth_controller.cc b/net/http/http_auth_controller.cc
index 9cc57de35aadec7396d8c383bc6584f93bc1fb90..69bbdfc74c3466892c721b15338ce44e9cd8ab4d 100644
--- a/net/http/http_auth_controller.cc
+++ b/net/http/http_auth_controller.cc
@@ -435,8 +435,12 @@ void HttpAuthController::InvalidateCurrentHandler(
 
   if (action == INVALIDATE_HANDLER_AND_CACHED_CREDENTIALS)
     InvalidateRejectedAuthFromCache();
-  if (action == INVALIDATE_HANDLER_AND_DISABLE_SCHEME)
+  if (action == INVALIDATE_HANDLER_AND_DISABLE_SCHEME) {
     DisableAuthScheme(handler_->auth_scheme());
+    // This scheme might have been tried with the default credentials, but
+    // the *next* one is still allowed to try them.
+    default_credentials_used_ = false;
+  }
   handler_.reset();
   identity_ = HttpAuth::Identity();
 }