Remove the flag which disables non NAT address migration.

net/quic/quic_connection.cc

Index: net/quic/quic_connection.cc
diff --git a/net/quic/quic_connection.cc b/net/quic/quic_connection.cc
index c96fb42e35ae04f687dda51e8b5badbab0137128..43442265e560d8f8decf11503f35227231aeada3 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -1364,17 +1364,6 @@ bool QuicConnection::ProcessValidatedPacket(const QuicPacketHeader& header) {
     return false;
   }
 
-  PeerAddressChangeType type = NO_CHANGE;
-  if (peer_ip_changed_ || peer_port_changed_) {
-    type = DeterminePeerAddressChangeType();
-    if (FLAGS_quic_disable_non_nat_address_migration && type != PORT_CHANGE &&
-        type != IPV4_SUBNET_CHANGE) {
-      SendConnectionCloseWithDetails(QUIC_ERROR_MIGRATING_ADDRESS,
-                                     "Invalid peer address migration.");
-      return false;
-    }
-  }
-
   if (!Near(header.packet_number, last_header_.packet_number)) {
     DVLOG(1) << ENDPOINT << "Packet " << header.packet_number
              << " out of bounds.  Discarding";
@@ -1429,6 +1418,7 @@ bool QuicConnection::ProcessValidatedPacket(const QuicPacketHeader& header) {
   DCHECK_EQ(NEGOTIATED_VERSION, version_negotiation_state_);
 
   if (peer_ip_changed_ || peer_port_changed_) {
+    PeerAddressChangeType type = DeterminePeerAddressChangeType();
     IPEndPoint old_peer_address = peer_address_;
     peer_address_ = IPEndPoint(
         peer_ip_changed_ ? migrating_peer_ip_ : peer_address_.address().bytes(),