Start using the loss timeout in QuicSentPacketManager and add a mock

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 4690f21deece01399eacc9a7c9c05528ca21722f..c8d5a90f287e3b1a496521ae2f732a119c89e23b 100644
--- a/net/quic/quic_sent_packet_manager.h
+++ b/net/quic/quic_sent_packet_manager.h
@@ -175,10 +175,18 @@ class NET_EXPORT_PRIVATE QuicSentPacketManager {
     NOT_RECEIVED_BY_PEER,
   };
 
+  // The retransmission timer is a single timer which switches modes depending
+  // upon connection state.
   enum RetransmissionTimeoutMode {
+    // A conventional TCP style RTO.
     RTO_MODE,
+    // A tail loss probe.  By default, QUIC sends up to two before RTOing.
     TLP_MODE,
+    // Retransmission of handshake packets prior to handshake completion.
     HANDSHAKE_MODE,
+    // Re-invoke the loss detection when a packet is not acked before the
+    // loss detection algorithm expects.
+    LOSS_MODE,
   };
 
   typedef linked_hash_map<QuicPacketSequenceNumber,