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

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/system_wrappers/include/field_trial.h"
+
 namespace webrtc {
 
 const char* kBweTypeHistogram = "WebRTC.BWE.Types";
+
+namespace congestion_controller {
+int GetMinBitrateBps() {
+  constexpr int kAudioMinBitrateBps = 5000;
+  constexpr int kMinBitrateBps = 10000;
+  if (webrtc::field_trial::FindFullName("WebRTC-Audio-SendSideBwe") ==
+      "Enabled") {
+    return kAudioMinBitrateBps;
+  }
+  return kMinBitrateBps;
+}
+
+}  // namespace congestion_controller
 }  // namespace webrtc