Add UMA for tracking which BWE versions are in use.

webrtc/modules/remote_bitrate_estimator/BUILD.gn

 # Copyright (c) 2014 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.
 
 import("../../build/webrtc.gni")
 import("//testing/test.gni")
 
 declare_args() {
   # Set this to true to enable BWE test logging.
   rtc_enable_bwe_test_logging = false
 }
 
 source_set("remote_bitrate_estimator") {
   sources = [
     "aimd_rate_control.cc",
     "aimd_rate_control.h",
+    "bwe_defines.cc",
     "include/bwe_defines.h",
     "include/remote_bitrate_estimator.h",
     "include/send_time_history.h",
     "inter_arrival.cc",
     "inter_arrival.h",
     "overuse_detector.cc",
     "overuse_detector.h",
     "overuse_estimator.cc",
     "overuse_estimator.h",
     "remote_bitrate_estimator_abs_send_time.cc",
@@ skipping 85 matching lines @@
     }
 
     deps = [
       "../../test:test_support",
       "../pacing",
       "//testing/gmock",
       "//testing/gtest",
     ]
   }
 }