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

chrome/browser/io_thread.cc

Index: chrome/browser/io_thread.cc
diff --git a/chrome/browser/io_thread.cc b/chrome/browser/io_thread.cc
index 2301ab5ab5965f00311c4b15320e022f4d42f313..e4cae67daf3401b4ab6421fb10d39ccbb078e012 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -1107,7 +1107,8 @@ void IOThread::InitializeNetworkSessionParamsFromGlobals(
   params->quic_connection_options = globals.quic_connection_options;
   globals.quic_close_sessions_on_ip_change.CopyToIfSet(
       &params->quic_close_sessions_on_ip_change);
-
+  globals.quic_migrate_sessions_on_net_change.CopyToIfSet(
+      &params->quic_migrate_sessions_on_net_change);
   globals.origin_to_force_quic_on.CopyToIfSet(
       &params->origin_to_force_quic_on);
   params->enable_user_alternate_protocol_ports =
@@ -1242,6 +1243,8 @@ void IOThread::ConfigureQuicGlobals(
         GetQuicConnectionOptions(command_line, quic_trial_params);
     globals->quic_close_sessions_on_ip_change.set(
         ShouldQuicCloseSessionsOnIpChange(quic_trial_params));
+    globals->quic_migrate_sessions_on_net_change.set(
+        ShouldQuicMigrateSessionsOnNetChange(quic_trial_params));
   }
 
   size_t max_packet_length = GetQuicMaxPacketLength(command_line,
@@ -1483,6 +1486,20 @@ bool IOThread::ShouldQuicCloseSessionsOnIpChange(
       "true");
 }
 
+bool IOThread::ShouldQuicMigrateSessionsOnNetChange(
+    const VariationParameters& quic_trial_params) {
+#if defined(OS_ANDROID)
+  &&base::android::BuildInfo::GetInstance()->sdk_int() >=
+      base::android::SDK_VERSION_LOLLIPOP
+      // Migration only implemented for Android versions >= L.

[Ryan Hamilton, 2015/11/17 14:37:10]

I was thinking about this. This code is here because NetworkChangeNotifier only
implements the high-resolution events on Lollipop, right? In that case, I think
NetworkChangeNotifier should have a method like SupportsHighResolutinEvents (or
whatever) and QuicStreamFactory should query that...

[Jana, 2015/11/18 04:31:41]

Yeah -- I hadn't done that yet. But you're right that if we do this in the
stream_factory, we don't need to do it here. I like your API, but I'm doing this
in the quic_stream_factory for now. Paul, I can add this API; do you think this
is a reasonable change to NetworkChangeNotifier?

[pauljensen, 2015/11/18 17:24:23]

ya, adding a NetworkChangeNotifier API for this SGTM.  I was going to propose
adding a net error code return value from the NCN::GetDefaultNetwork API: 
https://codereview.chromium.org/1416213003/diff/1/net/base/network_change_not...
but having a more general API seems like a good idea.

[Jana, 2015/11/18 21:44:17]

Yeah, I think this belongs in the NetworkChangeNotifier, because we'd want to
make a decision about which notifier to register for based on this query. I'll
get this in.

[Ryan Hamilton, 2015/11/18 22:23:35]

One idea might be to have NetworkChangeNotifier::AddNetworkObserver() return a
bool, which is false if the NetworkObserver is not supported?

[Jana, 2015/11/21 02:21:22]

Ongoing in https://codereview.chromium.org/1454313002/

+      return base::LowerCaseEqualsASCII(
+          GetVariationParam(quic_trial_params,
+                            "migrate_sessions_on_net_change"),
+          "true");
+#endif
+  return false;
+}

[Ryan Hamilton, 2015/11/17 04:57:27]

Since this code is conditional, I'm surprised the tests are not conditional on
#if android.

[Jana, 2015/11/18 04:31:41]

code's not conditional anymore, so tests should be fine.

+
 size_t IOThread::GetQuicMaxPacketLength(
     const base::CommandLine& command_line,
     const VariationParameters& quic_trial_params) {