Adds plumbing for QUIC early connection migration. No behavior change.

net/quic/quic_sent_packet_manager.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_QUIC_QUIC_SENT_PACKET_MANAGER_H_
 #define NET_QUIC_QUIC_SENT_PACKET_MANAGER_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 84 matching lines @@
   class NET_EXPORT_PRIVATE NetworkChangeVisitor {
    public:
     virtual ~NetworkChangeVisitor() {}
 
     // Called when congestion window may have changed.
     virtual void OnCongestionWindowChange() = 0;
 
     // Called when RTT may have changed, including when an RTT is read from
     // the config.
     virtual void OnRttChange() = 0;
+
+    // Called with the path may be degrading. Note that the path may only be
+    // temporarily degrading.
+    // TODO(jri): With multipath, this method should probably have a path_id
+    // parameter, and should maybe result in the path being marked as inactive.
+    virtual void OnPathDegrading() = 0;
   };
 
   QuicSentPacketManager(Perspective perspective,
                         QuicPathId path_id,
                         const QuicClock* clock,
                         QuicConnectionStats* stats,
                         CongestionControlType congestion_control_type,
                         LossDetectionType loss_type,
                         MultipathDelegateInterface* delegate);
   virtual ~QuicSentPacketManager();
@@ skipping 326 matching lines @@
   // Records bandwidth from server to client in normal operation, over periods
   // of time with no loss events.
   QuicSustainedBandwidthRecorder sustained_bandwidth_recorder_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicSentPacketManager);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_SENT_PACKET_MANAGER_H_