Add histograms to understand how often migration to new socket fails and why.

Bug: b/171063562
Change-Id: Ib17016732a59cb434855af3098288ec4147fb939
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2488700
Commit-Queue: Renjie Tang <renjietang@chromium.org>
Reviewed-by: David Schinazi <dschinazi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819186}

net/quic/quic_chromium_client_session.cc

@@ -135,6 +135,10 @@ void RecordConnectionCloseErrorCodeImpl(const std::string& histogram,
   }
 }
 
+void LogMigrateToSocketStatus(bool success) {
+  UMA_HISTOGRAM_BOOLEAN("Net.QuicSession.MigrateToSocketSuccess", success);
+}
+
 void RecordConnectionCloseErrorCode(const quic::QuicConnectionCloseFrame& frame,
                                     quic::ConnectionCloseSource source,
                                     const std::string& hostname,
@@ -865,6 +869,7 @@ QuicChromiumClientSession::QuicChromiumClientSession(
       max_allowed_push_id_(max_allowed_push_id),
       attempted_zero_rtt_(false),
       num_pings_sent_(0),
+      num_migrations_(0),
       push_promise_index_(std::move(push_promise_index)) {
   // Make sure connection migration and goaway on path degrading are not turned
   // on at the same time.
@@ -1875,6 +1880,7 @@ void QuicChromiumClientSession::OnConnectionClosed(
     UMA_HISTOGRAM_LONG_TIMES_100(
         "Net.QuicSession.ConnectionDuration",
         tick_clock_->NowTicks() - connect_timing_.connect_end);
+    UMA_HISTOGRAM_COUNTS_100("Net.QuicSession.NumMigrations", num_migrations_);
   } else {
     if (error == quic::QUIC_PUBLIC_RESET) {
       RecordHandshakeFailureReason(HANDSHAKE_FAILURE_PUBLIC_RESET);
@@ -2178,11 +2184,14 @@ void QuicChromiumClientSession::OnProbeSucceeded(
   // be acquired by connection and used as default on success.
   if (!MigrateToSocket(std::move(socket), std::move(reader),
                        std::move(writer))) {
+    LogMigrateToSocketStatus(false);
     net_log_.AddEvent(
         NetLogEventType::QUIC_CONNECTION_MIGRATION_FAILURE_AFTER_PROBING);
     return;
   }
 
+  LogMigrateToSocketStatus(true);
+
   // Notify the connection that migration succeeds after probing.
   if (connection()->IsPathDegrading())
     connection()->OnSuccessfulMigrationAfterProbing();
@@ -2190,6 +2199,7 @@ void QuicChromiumClientSession::OnProbeSucceeded(
   net_log_.AddEventWithInt64Params(
       NetLogEventType::QUIC_CONNECTION_MIGRATION_SUCCESS_AFTER_PROBING,
       "migrate_to_network", network);
+  num_migrations_++;
   HistogramAndLogMigrationSuccess(connection_id());
   if (network == default_network_) {
     DVLOG(1) << "Client successfully migrated to default network: "

net/quic/quic_chromium_client_session.h

@@ -930,6 +930,8 @@ class NET_EXPORT_PRIVATE QuicChromiumClientSession
 
   size_t num_pings_sent_;
 
+  size_t num_migrations_;
+
   std::unique_ptr<quic::QuicClientPushPromiseIndex> push_promise_index_;
 
   base::WeakPtrFactory<QuicChromiumClientSession> weak_factory_{this};

tools/metrics/histograms/histograms_xml/net/histograms.xml

@@ -2996,6 +2996,16 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Net.QuicSession.MigrateToSocketSuccess" enum="Boolean"
+    expires_after="2021-05-11">
+  <owner>renjietang@chromium.org</owner>
+  <owner>src/net/quic/OWNERS</owner>
+  <summary>
+    Records whether the migration of the QuicSession to a new socket is
+    successful.
+  </summary>
+</histogram>
+
 <histogram name="Net.QuicSession.MinRTT" units="ms" expires_after="2021-05-11">
   <owner>dschinazi@chromium.org</owner>
   <owner>src/net/quic/OWNERS</owner>
@@ -3024,6 +3034,13 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Net.QuicSession.NumMigrations" units="units"
+    expires_after="2021-05-11">
+  <owner>renjietang@chromium.org</owner>
+  <owner>src/net/quic/OWNERS</owner>
+  <summary>The number of successful migrations for a QUIC session.</summary>
+</histogram>
+
 <histogram name="Net.QuicSession.NumMigrationsExercisedBeforePublicReset"
     units="migrations" expires_after="2021-05-11">
   <owner>zhongyi@chromium.org</owner>