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

net/quic/core/quic_session.h

Index: net/quic/core/quic_session.h
diff --git a/net/quic/core/quic_session.h b/net/quic/core/quic_session.h
index bad3a738253df95ffc6453180850b1978833fc00..9310f9ad66ddc3bd1ab3c52eedcde83d68b51cfb 100644
--- a/net/quic/core/quic_session.h
+++ b/net/quic/core/quic_session.h
@@ -108,6 +108,15 @@ class QUIC_EXPORT_PRIVATE QuicSession : public QuicConnectionVisitorInterface,
   bool HasPendingHandshake() const override;
   bool HasOpenDynamicStreams() const override;
   void OnPathDegrading() override;
+  void SaveStreamData(QuicStreamId id,
+                      QuicIOVector iov,
+                      size_t iov_offset,
+                      QuicStreamOffset offset,
+                      QuicByteCount data_length) override;
+  bool WriteStreamData(QuicStreamId id,
+                       QuicStreamOffset offset,
+                       QuicByteCount data_length,
+                       QuicDataWriter* writer) override;
 
   // StreamNotifierInterface methods:
   void OnStreamFrameAcked(const QuicStreamFrame& frame,
@@ -269,6 +278,8 @@ class QUIC_EXPORT_PRIVATE QuicSession : public QuicConnectionVisitorInterface,
 
   bool use_stream_notifier() const { return use_stream_notifier_; }
 
+  bool streams_own_data() const { return streams_own_data_; }
+
  protected:
   using StaticStreamMap = QuicSmallMap<QuicStreamId, QuicStream*, 2>;
 
@@ -516,6 +527,10 @@ class QUIC_EXPORT_PRIVATE QuicSession : public QuicConnectionVisitorInterface,
   // This session is notified on every ack or loss.
   const bool use_stream_notifier_;
 
+  // Streams of this session own their outstanding data. Outstanding data here
+  // means sent data waiting to be acked.
+  const bool streams_own_data_;
+
   DISALLOW_COPY_AND_ASSIGN(QuicSession);
 };