Add support for HTTP/3 control stream.

Upon initialization, QuicSpdySession will create a write_unidirectional stream
and write stream type and settings when crypto handshake is completed.

The peer will receive the stream type and create a read_unidirectional stream
that reads the settings.

gfe-relnote: version 99 only. Not in prod.
PiperOrigin-RevId: 252650934
Change-Id: I708280eb94dea3d6eb7e54b96ce8ee91e2b8684f
diff --git a/quic/core/http/quic_receive_control_stream.h b/quic/core/http/quic_receive_control_stream.h
index a977f63..4e854ed 100644
--- a/quic/core/http/quic_receive_control_stream.h
+++ b/quic/core/http/quic_receive_control_stream.h
@@ -34,6 +34,8 @@
   // Implementation of QuicStream.
   void OnDataAvailable() override;
 
+  void SetUnblocked() { sequencer()->SetUnblocked(); }
+
  protected:
   // Called from HttpDecoderVisitor.
   bool OnSettingsFrameStart(Http3FrameLengths frame_lengths);