Implement basic WebTransport over HTTP/2 functionality.

This includes datagrams, closing session and draining session, but does not include streams yet.

PiperOrigin-RevId: 582768912

build/source_list.json

diff --git a/build/source_list.json b/build/source_list.json
index 165f594..42f3fbb 100644
--- a/build/source_list.json
+++ b/build/source_list.json
@@ -391,6 +391,7 @@
     "quiche/spdy/core/spdy_protocol.h",
     "quiche/spdy/core/zero_copy_output_buffer.h",
     "quiche/web_transport/complete_buffer_visitor.h",
+    "quiche/web_transport/encapsulated/encapsulated_web_transport.h",
     "quiche/web_transport/web_transport.h"
   ],
   "quiche_core_srcs": [
@@ -678,7 +679,8 @@
     "quiche/spdy/core/spdy_pinnable_buffer_piece.cc",
     "quiche/spdy/core/spdy_prefixed_buffer_reader.cc",
     "quiche/spdy/core/spdy_protocol.cc",
-    "quiche/web_transport/complete_buffer_visitor.cc"
+    "quiche/web_transport/complete_buffer_visitor.cc",
+    "quiche/web_transport/encapsulated/encapsulated_web_transport.cc"
   ],
   "quiche_tool_support_hdrs": [
     "quiche/common/platform/api/quiche_command_line_flags.h",
@@ -741,6 +743,7 @@
     "quiche/common/platform/api/quiche_test.h",
     "quiche/common/platform/api/quiche_test_loopback.h",
     "quiche/common/platform/api/quiche_test_output.h",
+    "quiche/common/test_tools/mock_streams.h",
     "quiche/common/test_tools/quiche_test_utils.h",
     "quiche/http2/adapter/mock_http2_visitor.h",
     "quiche/http2/adapter/recording_http2_visitor.h",
@@ -1072,6 +1075,7 @@
     "quiche/common/simple_buffer_allocator_test.cc",
     "quiche/common/structured_headers_generated_test.cc",
     "quiche/common/structured_headers_test.cc",
+    "quiche/common/test_tools/mock_streams_test.cc",
     "quiche/common/test_tools/quiche_test_utils_test.cc",
     "quiche/common/wire_serialization_test.cc",
     "quiche/http2/adapter/event_forwarder_test.cc",
@@ -1301,7 +1305,8 @@
     "quiche/spdy/core/spdy_intrusive_list_test.cc",
     "quiche/spdy/core/spdy_pinnable_buffer_piece_test.cc",
     "quiche/spdy/core/spdy_prefixed_buffer_reader_test.cc",
-    "quiche/spdy/core/spdy_protocol_test.cc"
+    "quiche/spdy/core/spdy_protocol_test.cc",
+    "quiche/web_transport/encapsulated/encapsulated_web_transport_test.cc"
   ],
   "io_tests_hdrs": [