Introduce HandshakeState enum to sent packet manager. Not used yet, not protected.

gfe-relnote: (n/a) add unused enum.
PiperOrigin-RevId: 280647693
Change-Id: Iaeb1e8aa12379f6558533eb457b3b4fe2790f0cb

quic/core/quic_sent_packet_manager.h

diff --git a/quic/core/quic_sent_packet_manager.h b/quic/core/quic_sent_packet_manager.h
index 1f2b3d2..4c2b429 100644
--- a/quic/core/quic_sent_packet_manager.h
+++ b/quic/core/quic_sent_packet_manager.h
@@ -107,6 +107,25 @@
     PTO_MODE,
   };
 
+  // Handshake state of this connection.
+  enum HandshakeState {
+    // Initial state.
+    HANDSHAKE_START,
+    // Only used in IETF QUIC with TLS handshake. State proceeds to
+    // HANDSHAKE_PROCESSED after a packet of HANDSHAKE packet number space
+    // gets successfully processed, and the initial key can be dropped.
+    HANDSHAKE_PROCESSED,
+    // In QUIC crypto, state proceeds to HANDSHAKE_COMPLETE if client receives
+    // SHLO or server successfully processes an ENCRYPTION_FORWARD_SECURE
+    // packet, such that the handshake packets can be neutered. In IETF QUIC
+    // with TLS handshake, state proceeds to HANDSHAKE_COMPLETE once the
+    // endpoint has both 1-RTT send and receive keys.
+    HANDSHAKE_COMPLETE,
+    // Only used in IETF QUIC with TLS handshake. State proceeds to
+    // HANDSHAKE_CONFIRMED if a 1-RTT packet gets acknowledged.
+    HANDSHAKE_CONFIRMED,
+  };
+
   QuicSentPacketManager(Perspective perspective,
                         const QuicClock* clock,
                         QuicRandom* random,