Turning off CID truncation for proxied connections.

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 f9c2e207a4dcfa12ce047f4471cb33e66971948d..f49b058c24999780bb6d936d4dbe3ba0feb22ea1 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -232,7 +232,8 @@ QuicConnection::QuicConnection(QuicConnectionId connection_id,
       peer_ip_changed_(false),
       peer_port_changed_(false),
       self_ip_changed_(false),
-      self_port_changed_(false) {
+      self_port_changed_(false),
+      can_truncate_connection_ids_(true) {
   DVLOG(1) << ENDPOINT << "Created connection with connection_id: "
            << connection_id;
   if (!FLAGS_quic_unified_timeouts) {
@@ -271,7 +272,8 @@ void QuicConnection::SetFromConfig(const QuicConfig& config) {
   }
   sent_packet_manager_.SetFromConfig(config);
   if (FLAGS_allow_truncated_connection_ids_for_quic &&
-      config.HasReceivedBytesForConnectionId()) {
+      config.HasReceivedBytesForConnectionId() &&
+      can_truncate_connection_ids_) {
     packet_generator_.SetConnectionIdLength(
         config.ReceivedBytesForConnectionId());
   }