Implement an end-to-end test for WebTransport negotiation.

PiperOrigin-RevId: 362632936
Change-Id: Ifd4a18fdb86f24bdcb7a043e3d318b4317b5dbae
diff --git a/quic/test_tools/quic_test_backend.cc b/quic/test_tools/quic_test_backend.cc
new file mode 100644
index 0000000..f33c6f1
--- /dev/null
+++ b/quic/test_tools/quic_test_backend.cc
@@ -0,0 +1,23 @@
+// Copyright (c) 2021 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "quic/test_tools/quic_test_backend.h"
+
+namespace quic {
+namespace test {
+
+QuicSimpleServerBackend::WebTransportResponse
+QuicTestBackend::ProcessWebTransportRequest(
+    const spdy::Http2HeaderBlock& request_headers) {
+  if (!SupportsWebTransport()) {
+    return QuicSimpleServerBackend::ProcessWebTransportRequest(request_headers);
+  }
+
+  WebTransportResponse response;
+  response.response_headers[":status"] = "200";
+  return response;
+}
+
+}  // namespace test
+}  // namespace quic