Add UMA for tracking which BWE versions are in use.

webrtc/modules/remote_bitrate_estimator/include/bwe_defines.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.
  */
 
 #ifndef WEBRTC_MODULES_REMOTE_BITRATE_ESTIMATOR_INCLUDE_BWE_DEFINES_H_
 #define WEBRTC_MODULES_REMOTE_BITRATE_ESTIMATOR_INCLUDE_BWE_DEFINES_H_
 
 #include "webrtc/base/optional.h"
 #include "webrtc/typedefs.h"
 
 #define BWE_MAX(a, b) ((a) > (b) ? (a) : (b))
 #define BWE_MIN(a, b) ((a) < (b) ? (a) : (b))
 
 namespace webrtc {
 
 static const int64_t kBitrateWindowMs = 1000;
 
+extern const char* kBweTypeHistogram;
+
+enum BweNames {
+  kReceiverNoExtension = 0,
+  kReceiverTOffset = 1,
+  kReceiverAbsSendTime = 2,
+  kSendSideTransportSeqNum = 3,
+  kBweNamesMax = 4
+};
+
 enum BandwidthUsage {
   kBwNormal = 0,
   kBwUnderusing = 1,
   kBwOverusing = 2,
 };
 
 enum RateControlState { kRcHold, kRcIncrease, kRcDecrease };
 
 enum RateControlRegion { kRcNearMax, kRcAboveMax, kRcMaxUnknown };
 
 struct RateControlInput {
   RateControlInput(BandwidthUsage bw_state,
                    const rtc::Optional<uint32_t>& incoming_bitrate,
                    double noise_var)
       : bw_state(bw_state),
         incoming_bitrate(incoming_bitrate),
         noise_var(noise_var) {}
 
   BandwidthUsage bw_state;
   rtc::Optional<uint32_t> incoming_bitrate;
   double noise_var;
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_REMOTE_BITRATE_ESTIMATOR_INCLUDE_BWE_DEFINES_H_