Add a test to ensure QUIC's TcpCubicSender always allows packets to be

net/quic/congestion_control/tcp_cubic_sender_test.cc

Index: net/quic/congestion_control/tcp_cubic_sender_test.cc
diff --git a/net/quic/congestion_control/tcp_cubic_sender_test.cc b/net/quic/congestion_control/tcp_cubic_sender_test.cc
index f6afdc8122852f3143930d9ba6ed9824cb87ae2a..c01e0c7498eaed0ec6c95bdf4e3a5eb4c6b1e259 100644
--- a/net/quic/congestion_control/tcp_cubic_sender_test.cc
+++ b/net/quic/congestion_control/tcp_cubic_sender_test.cc
@@ -21,7 +21,8 @@ using std::min;
 namespace net {
 namespace test {
 
-const uint32 kDefaultWindowTCP = 10 * kDefaultTCPMSS;
+const int64 kInitialCongestionWindow = 10;
+const uint32 kDefaultWindowTCP = kInitialCongestionWindow * kDefaultTCPMSS;
 
 // TODO(ianswett): Remove 10000 once b/10075719 is fixed.
 const QuicTcpCongestionWindow kDefaultMaxCongestionWindowTCP = 10000;
@@ -299,6 +300,19 @@ TEST_F(TcpCubicSenderTest, SlowStartPacketLoss) {
   EXPECT_FALSE(sender_->hybrid_slow_start().started());
 }
 
+TEST_F(TcpCubicSenderTest, NoPRRWhenLessThanOnePacketInFlight) {
+  SendAvailableSendWindow();
+  LoseNPackets(kInitialCongestionWindow - 1);
+  AckNPackets(1);
+  // PRR will allow 2 packets for every ack during recovery.
+  EXPECT_EQ(2, SendAvailableSendWindow());
+  // Simulate abandoning all packets by supplying a bytes_in_flight of 0.
+  // PRR should now allow a packet to be sent, even though prr's state
+  // variables believe it has sent enough packets.
+  EXPECT_EQ(QuicTime::Delta::Zero(),
+            sender_->TimeUntilSend(clock_.Now(), 0, HAS_RETRANSMITTABLE_DATA));
+}
+
 TEST_F(TcpCubicSenderTest, SlowStartPacketLossPRR) {
   // Test based on the first example in RFC6937.
   // Ack 10 packets in 5 acks to raise the CWND to 20, as in the example.