Fix a bug where QUIC ack frames were not bundled with crypto stream

net/quic/quic_packet_generator.cc

Index: net/quic/quic_packet_generator.cc
diff --git a/net/quic/quic_packet_generator.cc b/net/quic/quic_packet_generator.cc
index 952bdc266df9333e60e425f012cd2d2e72a6bcb6..9e7473ebbf06fd39f9cd6ad85daac74f02d86509 100644
--- a/net/quic/quic_packet_generator.cc
+++ b/net/quic/quic_packet_generator.cc
@@ -97,7 +97,11 @@ QuicConsumedData QuicPacketGenerator::ConsumeData(QuicStreamId id,
                                                   FecProtection fec_protection,
                                                   QuicAckNotifier* notifier) {
   IsHandshake handshake = id == kCryptoStreamId ? IS_HANDSHAKE : NOT_HANDSHAKE;
-  SendQueuedFrames(false);
+  // To make reasoning about crypto frames easier, we don't combine them with
+  // other retransmittable frames in a single packet.
+  const bool flush = handshake == IS_HANDSHAKE &&
+      packet_creator_.HasPendingRetransmittableFrames();
+  SendQueuedFrames(flush);
 
   size_t total_bytes_consumed = 0;
   bool fin_consumed = false;
@@ -155,6 +159,11 @@ QuicConsumedData QuicPacketGenerator::ConsumeData(QuicStreamId id,
     }
   }
 
+  // Don't allow the handshake to be bundled with other retransmittable frames.
+  if (handshake == IS_HANDSHAKE) {
+    SendQueuedFrames(true);
+  }
+
   // Try to close FEC group since we've either run out of data to send or we're
   // blocked. If not in batch mode, force close the group.
   MaybeSendFecPacketAndCloseGroup(!InBatchMode());