Implement a QUIC No PRR connection option, NPRR. Protected by FLAGS_quic_allow_no_prr

net/quic/congestion_control/tcp_cubic_sender_bytes_test.cc

Index: net/quic/congestion_control/tcp_cubic_sender_bytes_test.cc
diff --git a/net/quic/congestion_control/tcp_cubic_sender_bytes_test.cc b/net/quic/congestion_control/tcp_cubic_sender_bytes_test.cc
index d790f6239076738062639baebe22e70c5e1d4902..e845f3e181f9184c47e307f7023d550f7cc431c7 100644
--- a/net/quic/congestion_control/tcp_cubic_sender_bytes_test.cc
+++ b/net/quic/congestion_control/tcp_cubic_sender_bytes_test.cc
@@ -780,6 +780,36 @@ TEST_F(TcpCubicSenderBytesTest, PaceBelowCWND) {
       sender_->TimeUntilSend(QuicTime::Zero(), 4 * kDefaultTCPMSS).IsZero());
 }
 
+TEST_F(TcpCubicSenderBytesTest, NoPRR) {
+  ValueRestore<bool> old_flag(&FLAGS_quic_allow_noprr, true);
+  QuicTime::Delta rtt = QuicTime::Delta::FromMilliseconds(100);
+  sender_->rtt_stats_.UpdateRtt(rtt, QuicTime::Delta::Zero(), QuicTime::Zero());
+
+  sender_->SetNumEmulatedConnections(1);
+  // Verify that kCOPT: kNPRR allows all packets to be sent, even if only one
+  // ack has been received.
+  QuicTagVector options;
+  options.push_back(kNPRR);
+  QuicConfig config;
+  QuicConfigPeer::SetReceivedConnectionOptions(&config, options);
+  sender_->SetFromConfig(config, Perspective::IS_SERVER);
+  SendAvailableSendWindow();
+  LoseNPackets(9);
+  AckNPackets(1);
+
+  // We should now have fallen out of slow start with a reduced window.
+  EXPECT_EQ(kRenoBeta * kDefaultWindowTCP, sender_->GetCongestionWindow());
+  const QuicPacketCount window_in_packets =
+      kRenoBeta * kDefaultWindowTCP / kDefaultTCPMSS;
+  const QuicBandwidth expected_pacing_rate =
+      QuicBandwidth::FromBytesAndTimeDelta(kRenoBeta * kDefaultWindowTCP,
+                                           sender_->rtt_stats_.smoothed_rtt());
+  EXPECT_EQ(expected_pacing_rate, sender_->PacingRate());
+  EXPECT_EQ(window_in_packets,
+            static_cast<uint64_t>(SendAvailableSendWindow()));
+  EXPECT_EQ(expected_pacing_rate, sender_->PacingRate());
+}
+
 TEST_F(TcpCubicSenderBytesTest, ResetAfterConnectionMigration) {
   // Starts from slow start.
   sender_->SetNumEmulatedConnections(1);