Only set one QUIC sending alarm at once. Flag protected by --quic_only_one_sending_alarm.

net/quic/quic_sent_packet_manager.h

Index: net/quic/quic_sent_packet_manager.h
diff --git a/net/quic/quic_sent_packet_manager.h b/net/quic/quic_sent_packet_manager.h
index 26df05981d9e1908503f3d9ee6cd995117bb4724..7ddcae184c1f83dd8a1a965b699cd72f3382958c 100644
--- a/net/quic/quic_sent_packet_manager.h
+++ b/net/quic/quic_sent_packet_manager.h
@@ -241,6 +241,8 @@ class NET_EXPORT_PRIVATE QuicSentPacketManager {
 
   bool using_pacing() const { return using_pacing_; }
 
+  bool handshake_confirmed() const { return handshake_confirmed_; }
+
   void set_debug_delegate(DebugDelegate* debug_delegate) {
     debug_delegate_ = debug_delegate;
   }