Deprecate rolled out flag: FLAGS_quic_allow_port_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 383db69e135b97068c40ede17bd99a01ade45e90..f40b34dfe590af5b07e40d2d6115ad8c8e69a2ba 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -1179,17 +1179,15 @@ void QuicConnection::WriteIfNotBlocked() {
 }
 
 bool QuicConnection::ProcessValidatedPacket() {
-  if ((!FLAGS_quic_allow_port_migration && peer_port_changed_) ||
-      peer_ip_changed_ || self_ip_changed_ || self_port_changed_) {
+  if (peer_ip_changed_ || self_ip_changed_ || self_port_changed_) {
     SendConnectionCloseWithDetails(
         QUIC_ERROR_MIGRATING_ADDRESS,
         "Neither IP address migration, nor self port migration are supported.");
     return false;
   }
 
-  // Port migration is supported, do it now if port has changed.
-  if (FLAGS_quic_allow_port_migration &&
-      peer_port_changed_) {
+  // Peer port migration is supported, do it now if port has changed.
+  if (peer_port_changed_) {
     DVLOG(1) << ENDPOINT << "Peer's port changed from "
              << peer_address_.port() << " to " << migrating_peer_port_
              << ", migrating connection.";