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

net/quic/quic_config.h

Index: net/quic/quic_config.h
diff --git a/net/quic/quic_config.h b/net/quic/quic_config.h
index bd6e5d8a75749744248834ae545b19a6425a4ab9..6650f7434dded252999a14534a0c7681d8d739e2 100644
--- a/net/quic/quic_config.h
+++ b/net/quic/quic_config.h
@@ -335,6 +335,10 @@ class NET_EXPORT_PRIVATE QuicConfig {
 
   bool MultipathEnabled() const;
 
+  void SetDisableConnectionMigration();
+
+  bool DisableConnectionMigration() const;
+
   bool negotiated() const;
 
   // ToHandshakeMessage serialises the settings in this object as a series of
@@ -384,6 +388,9 @@ class NET_EXPORT_PRIVATE QuicConfig {
 
   // Whether to support multipath for this connection.
   QuicNegotiableUint32 multipath_enabled_;
+
+  // Whether tell peer not to attempt connection migration.
+  QuicFixedUint32 connection_migration_disabled_;
 };
 
 }  // namespace net