Disable connection migration if disabled in config sent by server.

components/domain_reliability/quic_error_mapping.cc

Index: components/domain_reliability/quic_error_mapping.cc
diff --git a/components/domain_reliability/quic_error_mapping.cc b/components/domain_reliability/quic_error_mapping.cc
index 0245ed08e98dbb50140db7b254d0403398bba546..0334fdc3528168d85b6c2eead5e0c1c0c17f0e6a 100644
--- a/components/domain_reliability/quic_error_mapping.cc
+++ b/components/domain_reliability/quic_error_mapping.cc
@@ -219,6 +219,11 @@ const struct QuicErrorMapping {
   // Network changed, but connection had one or more non-migratable streams.
   { net::QUIC_CONNECTION_MIGRATION_NON_MIGRATABLE_STREAM,
     "quic.connection_migration_non_migratable_stream" },
+  // Connection migration was not attempted because it was disabled in the
+  // received config.
+  { net::QUIC_CONNECTION_MIGRATION_DISABLED,
+    "quic.connection_migration_disabled" },
+
   // Stream frame overlaps with buffered data.
   { net::QUIC_OVERLAPPING_STREAM_DATA,
     "quic.overlapping_stream_data" },