Fix data race in channel_send.cc

'configured_bitrate_bps_' is accessed from different threads in
SetBitrate and GetBitrate (one comes back from OnNetworkRouteChange
callback, the other one is used in GetStats()) and so it should be
protected by a critical section.

Bug: webrtc:10010
Change-Id: I029baa729e0203b9f2d180d8835d61add26e6cef
Reviewed-on: https://webrtc-review.googlesource.com/c/111281
Commit-Queue: Peter Slatala <psla@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25675}
diff --git a/audio/channel_send.cc b/audio/channel_send.cc
index abdb980..a8b93cc 100644
--- a/audio/channel_send.cc
+++ b/audio/channel_send.cc
@@ -641,6 +641,7 @@
 }
 
 void ChannelSend::SetBitRate(int bitrate_bps, int64_t probing_interval_ms) {
+  rtc::CritScope lock(&bitrate_crit_section_);
   audio_coding_->ModifyEncoder([&](std::unique_ptr<AudioEncoder>* encoder) {
     if (*encoder) {
       (*encoder)->OnReceivedUplinkBandwidth(bitrate_bps, probing_interval_ms);
@@ -651,6 +652,7 @@
 }
 
 int ChannelSend::GetBitRate() const {
+  rtc::CritScope lock(&bitrate_crit_section_);
   return configured_bitrate_bps_;
 }