Fix issue with deprecated CongestionController interface not working.

webrtc/modules/congestion_controller/include/congestion_controller.h

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 29 matching lines @@
 
 class CongestionController : public CallStatsObserver, public Module {
  public:
   // Observer class for bitrate changes announced due to change in bandwidth
   // estimate or due to that the send pacer is full. Fraction loss and rtt is
   // also part of this callback to allow the observer to optimize its settings
   // for different types of network environments. The bitrate does not include
   // packet headers and is measured in bits per second.
   class Observer {
    public:
-    // This is to be deprecated. Please use the one below instead.
-    RTC_DEPRECATED virtual void OnNetworkChanged(uint32_t bitrate_bps,
-                                                 uint8_t fraction_loss,
-                                                 int64_t rtt_ms) {}
-
-    // TODO(minyue): make this method pure virtual when all uses of the old API
-    // have been updated.
     virtual void OnNetworkChanged(uint32_t bitrate_bps,
                                   uint8_t fraction_loss,  // 0 - 255.
                                   int64_t rtt_ms,
-                                  int64_t probing_interval_ms) {}
+                                  int64_t probing_interval_ms) = 0;
 
    protected:
     virtual ~Observer() {}
   };
   CongestionController(Clock* clock,
                        Observer* observer,
                        RemoteBitrateObserver* remote_bitrate_observer,
                        RtcEventLog* event_log,
                        PacketRouter* packet_router);
   // TODO(nisse): Deprecated. Will create and own a PacketRouter.
@@ skipping 79 matching lines @@
   uint8_t last_reported_fraction_loss_ GUARDED_BY(critsect_);
   int64_t last_reported_rtt_ GUARDED_BY(critsect_);
   NetworkState network_state_ GUARDED_BY(critsect_);
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(CongestionController);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_CONGESTION_CONTROLLER_INCLUDE_CONGESTION_CONTROLLER_H_