Set min BWE bitrate form 10kbps to 5kbps and centralize minimum bitrate.

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 36 matching lines @@
   // packet headers and is measured in bits per second.
   class Observer {
    public:
     virtual void OnNetworkChanged(uint32_t bitrate_bps,
                                   uint8_t fraction_loss,  // 0 - 255.
                                   int64_t rtt_ms) = 0;
 
    protected:
     virtual ~Observer() {}
   };
+
+  static int GetMinBitrateBps();

[stefan-webrtc, 2016/11/01 09:09:15]

I find it slightly weird that we expose this in the congestion controller
interface, as it's basically only used within the congestion controller
implementation. As I see it, CongestionController is implemented using the
classes in modules/bitrate_controller, modules/remote_bitrate_estimator,
modules/pacing, etc. I think we may end up moving all of those into
modules/congestion_controller down the line.

There may not be a better place for it right now though... Any suggestions?
Otherwise we'll go ahead with this.

[michaelt, 2016/11/01 09:21:55]

Moving the CongestionController related classes in to
modules/congestion_controller sounds like a good idea.

At the moment I see no better place to define GetMinBitrateBps. We may pass in
future the value down, or remove it in some places. So that we don't have to
define it globally. 

+
   CongestionController(Clock* clock,
                        Observer* observer,
                        RemoteBitrateObserver* remote_bitrate_observer,
                        RtcEventLog* event_log);
   CongestionController(Clock* clock,
                        Observer* observer,
                        RemoteBitrateObserver* remote_bitrate_observer,
                        RtcEventLog* event_log,
                        std::unique_ptr<PacketRouter> packet_router,
                        std::unique_ptr<PacedSender> pacer);
@@ skipping 65 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_