Make the masque client return a special error when it gets an expected failure

This allows the gateway response handler to return a testable exception that we look for in the run masque client method.

PiperOrigin-RevId: 848204801

quiche/quic/masque/masque_ohttp_client.cc

diff --git a/quiche/quic/masque/masque_ohttp_client.cc b/quiche/quic/masque/masque_ohttp_client.cc
index 65ef668..af08e1c 100644
--- a/quiche/quic/masque/masque_ohttp_client.cc
+++ b/quiche/quic/masque/masque_ohttp_client.cc
@@ -301,9 +301,9 @@
   auto cleanup =
       absl::MakeCleanup([this, it]() { pending_ohttp_requests_.erase(it); });
   QUICHE_RETURN_IF_ERROR(response.status());
+  QUICHE_RETURN_IF_ERROR(CheckGatewayResponse(*response));
   QUICHE_RETURN_IF_ERROR(
       CheckStatusAndContentType(*response, "message/ohttp-res"));
-  QUICHE_RETURN_IF_ERROR(CheckGatewayResponse(*response));
   absl::StatusOr<BinaryHttpResponse> binary_response =
       TryExtractBinaryResponse(request_id, it->second, *response);
   QUICHE_RETURN_IF_ERROR(binary_response.status());