Use QUICHE-provided mocks for WebTransport APIs.

PiperOrigin-RevId: 513326886

quiche/web_transport/test_tools/mock_web_transport.h

diff --git a/quiche/web_transport/test_tools/mock_web_transport.h b/quiche/web_transport/test_tools/mock_web_transport.h
index 0e05cda..a24cc7a 100644
--- a/quiche/web_transport/test_tools/mock_web_transport.h
+++ b/quiche/web_transport/test_tools/mock_web_transport.h
@@ -68,7 +68,7 @@
   MOCK_METHOD(Stream*, OpenOutgoingUnidirectionalStream, (), (override));
   MOCK_METHOD(DatagramStatus, SendOrQueueDatagram, (absl::string_view datagram),
               (override));
-  MOCK_METHOD(size_t, GetMaxDatagramSize, (), (const, override));
+  MOCK_METHOD(uint64_t, GetMaxDatagramSize, (), (const, override));
   MOCK_METHOD(void, SetDatagramMaxTimeInQueue,
               (absl::Duration max_time_in_queue), (override));
 };