Introduce support for basic WebTransport stats.

PiperOrigin-RevId: 564426331

build/source_list.json

diff --git a/build/source_list.json b/build/source_list.json
index 22ece80..f41f490 100644
--- a/build/source_list.json
+++ b/build/source_list.json
@@ -346,6 +346,7 @@
     "quiche/quic/core/uber_quic_stream_id_manager.h",
     "quiche/quic/core/uber_received_packet_manager.h",
     "quiche/quic/core/web_transport_interface.h",
+    "quiche/quic/core/web_transport_stats.h",
     "quiche/quic/platform/api/quic_bug_tracker.h",
     "quiche/quic/platform/api/quic_client_stats.h",
     "quiche/quic/platform/api/quic_export.h",
@@ -658,6 +659,7 @@
     "quiche/quic/core/tls_server_handshaker.cc",
     "quiche/quic/core/uber_quic_stream_id_manager.cc",
     "quiche/quic/core/uber_received_packet_manager.cc",
+    "quiche/quic/core/web_transport_stats.cc",
     "quiche/quic/platform/api/quic_socket_address.cc",
     "quiche/spdy/core/array_output_buffer.cc",
     "quiche/spdy/core/hpack/hpack_constants.cc",