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

net/quic/congestion_control/pacing_sender.cc

Index: net/quic/congestion_control/pacing_sender.cc
diff --git a/net/quic/congestion_control/pacing_sender.cc b/net/quic/congestion_control/pacing_sender.cc
index 405afdaaf204e44669124a3ba12a36efb5f0b928..14a72e5de595164061d324f7c6e4005241877f86 100644
--- a/net/quic/congestion_control/pacing_sender.cc
+++ b/net/quic/congestion_control/pacing_sender.cc
@@ -41,10 +41,6 @@ void PacingSender::OnCongestionEvent(bool rtt_updated,
   if (rtt_updated) {
     has_valid_rtt_ = true;
   }
-  if (bytes_in_flight == 0) {
-    // Add more burst tokens anytime the connection is entering quiescence.
-    burst_tokens_ = initial_packet_burst_;
-  }
   sender_->OnCongestionEvent(
       rtt_updated, bytes_in_flight, acked_packets, lost_packets);
 }
@@ -121,6 +117,10 @@ QuicTime::Delta PacingSender::TimeUntilSend(
     // Don't pace if we don't have an updated RTT estimate.
     return time_until_send;
   }
+  if (bytes_in_flight == 0) {
+    // Add more burst tokens anytime the connection is entering quiescence.
+    burst_tokens_ = initial_packet_burst_;
+  }
   if (burst_tokens_ > 0) {
     // Don't pace if we have burst tokens available.
     return time_until_send;