Stub for BBRv2, based on TCP congestion feedback frames.

net/quic/quic_protocol.h

Index: net/quic/quic_protocol.h
diff --git a/net/quic/quic_protocol.h b/net/quic/quic_protocol.h
index 9a076b5e14b73e1ffd452d255f321105795b5f43..93236bb2221a4e758b91506d780b74590ce11bf7 100644
--- a/net/quic/quic_protocol.h
+++ b/net/quic/quic_protocol.h
@@ -57,6 +57,8 @@ const QuicByteCount kDefaultMaxPacketSize = 1200;
 // additional 8 bytes.  This is a total overhead of 48 bytes.  Ethernet's
 // max packet size is 1500 bytes,  1500 - 48 = 1452.
 const QuicByteCount kMaxPacketSize = 1452;
+// Default maximum packet size used in Linux TCP implementations.
+const QuicByteCount kDefaultTCPMSS = 1460;
 
 // Maximum size of the initial congestion window in packets.
 const size_t kDefaultInitialWindow = 10;
@@ -689,6 +691,7 @@ enum CongestionFeedbackType {
   kTCP,  // Used to mimic TCP.
   kInterArrival,  // Use additional inter arrival information.
   kFixRate,  // Provided for testing.
+  kTCPBBR,  // BBR implementation based on TCP congestion feedback.
 };
 
 enum LossDetectionType {