Remove QUIC_VERSION_15 now that Chrome Stable supports QUIC_VERSION_16.

net/quic/quic_connection.cc

Index: net/quic/quic_connection.cc
diff --git a/net/quic/quic_connection.cc b/net/quic/quic_connection.cc
index 2a091ca604552821cce8348785155502156f8cee..0548c0cef4aee09f3510913939a1269f475af88e 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -551,9 +551,6 @@ void QuicConnection::ProcessAckFrame(const QuicAckFrame& incoming_ack) {
   largest_seen_packet_with_ack_ = last_header_.packet_sequence_number;
   received_packet_manager_.UpdatePacketInformationReceivedByPeer(
       incoming_ack.received_info);
-  if (version() <= QUIC_VERSION_15) {
-    ProcessStopWaitingFrame(incoming_ack.sent_info);
-  }
 
   sent_entropy_manager_.ClearEntropyBefore(
       received_packet_manager_.least_packet_awaited_by_peer() - 1);
@@ -642,12 +639,6 @@ bool QuicConnection::ValidateAckFrame(const QuicAckFrame& incoming_ack) {
     return false;
   }
 
-  if (version() <= QUIC_VERSION_15) {
-    if (!ValidateStopWaitingFrame(incoming_ack.sent_info)) {
-      return false;
-    }
-  }
-
   if (!incoming_ack.received_info.missing_packets.empty() &&
       *incoming_ack.received_info.missing_packets.rbegin() >
       incoming_ack.received_info.largest_observed) {
@@ -905,7 +896,6 @@ QuicAckFrame* QuicConnection::CreateAckFrame() {
   QuicAckFrame* outgoing_ack = new QuicAckFrame();
   received_packet_manager_.UpdateReceivedPacketInfo(
       &(outgoing_ack->received_info), clock_->ApproximateNow());
-  UpdateStopWaiting(&(outgoing_ack->sent_info));
   DVLOG(1) << ENDPOINT << "Creating ack frame: " << *outgoing_ack;
   return outgoing_ack;
 }
@@ -1583,7 +1573,7 @@ void QuicConnection::SendPing() {
   if (retransmission_alarm_->IsSet()) {
     return;
   }
-  if (version() <= QUIC_VERSION_16) {
+  if (version() == QUIC_VERSION_16) {
     // TODO(rch): remove this when we remove version 15 and 16.
     // This is a horrible hideous hack which we should not support.
     IOVector data;
@@ -1614,8 +1604,7 @@ void QuicConnection::SendAck() {
     send_feedback = true;
   }
 
-  packet_generator_.SetShouldSendAck(send_feedback,
-                                     version() > QUIC_VERSION_15);
+  packet_generator_.SetShouldSendAck(send_feedback, true);
 }
 
 void QuicConnection::OnRetransmissionTimeout() {