Add UMA for tracking which BWE versions are in use.

webrtc/modules/remote_bitrate_estimator/bwe_defines.cc

 /*
  *  Copyright (c) 2016 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.
  */
-
-#include "webrtc/modules/audio_coding/neteq/packet.h"
-
 namespace webrtc {
 
-Packet::Packet() = default;
-
-Packet::~Packet() = default;
-
+const char* kBweTypeHistogram = "WebRTC.BWE.Types";
 }  // namespace webrtc