Add a QuicConfig option to ask the client not to attempt migration.

net/quic/crypto/crypto_protocol.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_QUIC_CRYPTO_CRYPTO_PROTOCOL_H_
 #define NET_QUIC_CRYPTO_CRYPTO_PROTOCOL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 84 matching lines @@
 const QuicTag k5RTO = TAG('5', 'R', 'T', 'O');   // Close connection on 5 RTOs
 
 // Optional support of truncated Connection IDs.  If sent by a peer, the value
 // is the minimum number of bytes allowed for the connection ID sent to the
 // peer.
 const QuicTag kTCID = TAG('T', 'C', 'I', 'D');   // Connection ID truncation.
 
 // Multipath option.
 const QuicTag kMPTH = TAG('M', 'P', 'T', 'H');   // Enable multipath.
 
+const QuicTag kNCMR = TAG('N', 'C', 'M', 'R');   // Do not attempt connection
+                                                 // migration.
+
 // Enable bandwidth resumption experiment.
 const QuicTag kBWRE = TAG('B', 'W', 'R', 'E');  // Bandwidth resumption.
 const QuicTag kBWMX = TAG('B', 'W', 'M', 'X');  // Max bandwidth resumption.
 const QuicTag kBWRS = TAG('B', 'W', 'R', 'S');  // Server bandwidth resumption.
 
 // Enable path MTU discovery experiment.
 const QuicTag kMTUH = TAG('M', 'T', 'U', 'H');  // High-target MTU discovery.
 const QuicTag kMTUL = TAG('M', 'T', 'U', 'L');  // Low-target MTU discovery.
 
 // Proof types (i.e. certificate types)
@@ skipping 105 matching lines @@
 // amplification factor of any mirror DoS attack.
 //
 // A client may pad an inchoate client hello to a size larger than
 // kClientHelloMinimumSize to make it more likely to receive a complete
 // rejection message.
 const size_t kClientHelloMinimumSize = 1024;
 
 }  // namespace net
 
 #endif  // NET_QUIC_CRYPTO_CRYPTO_PROTOCOL_H_