Migrates QUIC sessions to a new network when old network is (about to be) disconnected.

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
diff --git a/chrome/browser/io_thread.h b/chrome/browser/io_thread.h
index 5c99d566e33313c7777b27c68dab477e8221ab81..e71f26cac533c91e72867fa72579b61d2b7221bd 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -241,6 +241,7 @@ class IOThread : public content::BrowserThreadDelegate {
     Optional<int> quic_idle_connection_timeout_seconds;
     Optional<bool> quic_disable_preconnect_if_0rtt;
     std::unordered_set<std::string> quic_host_whitelist;
+    Optional<bool> quic_migrate_sessions_on_network_change;
     bool enable_user_alternate_protocol_ports;
     // NetErrorTabHelper uses |dns_probe_service| to send DNS probes when a
     // main frame load fails with a DNS error in order to provide more useful
@@ -468,6 +469,11 @@ class IOThread : public content::BrowserThreadDelegate {
       const base::CommandLine& command_line,
       const VariationParameters& quic_trial_params);
 
+  // Returns true if QUIC should migrate sessions when primary network
+  // changes.
+  static bool ShouldQuicMigrateSessionsOnNetworkChange(
+      const VariationParameters& quic_trial_params);
+
   // Returns the maximum length for QUIC packets, based on any flags in
   // |command_line| or the field trial.  Returns 0 if there is an error
   // parsing any of the options, or if the default value should be used.