Add UMA for tracking which BWE versions are in use.

webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator.gypi

 # Copyright (c) 2011 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.
 
 {
   'includes': [
@@ skipping 10 matching lines @@
       'dependencies': [
         '<(webrtc_root)/common.gyp:webrtc_common',
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
       ],
       'sources': [
         'include/bwe_defines.h',
         'include/remote_bitrate_estimator.h',
         'include/send_time_history.h',
         'aimd_rate_control.cc',
         'aimd_rate_control.h',
+        'bwe_defines.cc',
         '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',
         'remote_bitrate_estimator_abs_send_time.h',
         'remote_bitrate_estimator_single_stream.cc',
         'remote_bitrate_estimator_single_stream.h',
@@ skipping 121 matching lines @@
             ],
           },
           'sources': [
             'tools/bwe_rtp_play.cc',
           ], # source
         },
       ],
     }],  # include_tests==1
   ],
 }