Early connection migration in QUIC.

net/quic/quic_stream_factory.h

Index: net/quic/quic_stream_factory.h
diff --git a/net/quic/quic_stream_factory.h b/net/quic/quic_stream_factory.h
index 93249ed2d4f2bc8f659f23094d8f2c5db2ae4208..2fc4c3074e5e5106ed56987a02e753a04d2c40d5 100644
--- a/net/quic/quic_stream_factory.h
+++ b/net/quic/quic_stream_factory.h
@@ -152,6 +152,7 @@ class NET_EXPORT_PRIVATE QuicStreamFactory
       bool disable_quic_on_timeout_with_open_streams,
       int idle_connection_timeout_seconds,
       bool migrate_sessions_on_network_change,
+      bool migrate_sessions_early,
       const QuicTagVector& connection_options);
   ~QuicStreamFactory() override;
 
@@ -502,6 +503,10 @@ class NET_EXPORT_PRIVATE QuicStreamFactory
   // interface changes.
   const bool migrate_sessions_on_network_change_;
 
+  // Set if early migration should be attempted when the connection
+  // experiences poor connectivity.
+  const bool migrate_sessions_early_;
+
   // Each profile will (probably) have a unique port_seed_ value.  This value
   // is used to help seed a pseudo-random number generator (PortSuggester) so
   // that we consistently (within this profile) suggest the same ephemeral