Fix a newly introduced bug in QUIC's PacingSender where burst_tokens_

net/quic/congestion_control/pacing_sender_test.cc

Index: net/quic/congestion_control/pacing_sender_test.cc
diff --git a/net/quic/congestion_control/pacing_sender_test.cc b/net/quic/congestion_control/pacing_sender_test.cc
index ba867b5ff16b8faecbd2e71878a5142478ba6338..1d1fe8f548ff989a4dfe8003e25f391c4f67b2f6 100644
--- a/net/quic/congestion_control/pacing_sender_test.cc
+++ b/net/quic/congestion_control/pacing_sender_test.cc
@@ -237,10 +237,17 @@ TEST_F(PacingSenderTest, InitialBurst) {
   clock_.AdvanceTime(QuicTime::Delta::FromMilliseconds(5));
   CheckPacketIsSentImmediately();
 
-  // Now reduce bytes in flight back to 0 by and ensure another burst of 10 can
-  // be sent.
-  EXPECT_CALL(*mock_sender_, OnCongestionEvent(true, 0, _, _));
-  pacing_sender_->OnCongestionEvent(true, 0, empty_map, empty_map);
+  // Next time TimeUntilSend is called with no bytes in flight, the tokens
+  // should be refilled and there should be no delay.
+  EXPECT_CALL(*mock_sender_,
+              TimeUntilSend(clock_.Now(),
+                            0,
+                            HAS_RETRANSMITTABLE_DATA)).
+      WillOnce(Return(zero_time_));
+  EXPECT_EQ(zero_time_,
+            pacing_sender_->TimeUntilSend(clock_.Now(),
+                                          0,
+                                          HAS_RETRANSMITTABLE_DATA));
   for (int i = 0 ; i < 10; ++i) {
     CheckPacketIsSentImmediately();
   }