In QUIC, send data is copied to streams rather than frames. Protected by FLAGS_quic_reloadable_flag…

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index b4af1e1add2ef4178cf56ba3833cf41e612c2c42..273e018d31efa13c6ea46add7660c2555db098c5 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -1312,6 +1312,9 @@ component("net") {
       "quic/core/quic_spdy_stream.h",
       "quic/core/quic_stream.cc",
       "quic/core/quic_stream.h",
+      "quic/core/quic_stream_frame_data_producer",
+      "quic/core/quic_stream_send_buffer.cc",
+      "quic/core/quic_stream_send_buffer.h",
       "quic/core/quic_stream_sequencer.cc",
       "quic/core/quic_stream_sequencer.h",
       "quic/core/quic_stream_sequencer_buffer.cc",
@@ -3096,6 +3099,8 @@ source_set("quic_test_tools") {
     "quic/test_tools/quic_time_wait_list_manager_peer.h",
     "quic/test_tools/rtt_stats_peer.cc",
     "quic/test_tools/rtt_stats_peer.h",
+    "quic/test_tools/simple_data_producer.cc",
+    "quic/test_tools/simple_data_producer.h",
     "quic/test_tools/simple_quic_framer.cc",
     "quic/test_tools/simple_quic_framer.h",
     "quic/test_tools/simulator/actor.cc",
@@ -4896,6 +4901,7 @@ test("net_unittests") {
     "quic/core/quic_framer_test.cc",
     "quic/core/quic_header_list_test.cc",
     "quic/core/quic_headers_stream_test.cc",
+    "quic/core/quic_stream_send_buffer_test.cc",
     "quic/test_tools/quic_test_utils_test.cc",
     "quic/test_tools/simulator/quic_endpoint_test.cc",
     "quic/test_tools/simulator/simulator_test.cc",