Resolves race between Channel::ProcessAndEncodeAudio() and Channel::StopSend()

webrtc/voice_engine/channel.h

Index: webrtc/voice_engine/channel.h
diff --git a/webrtc/voice_engine/channel.h b/webrtc/voice_engine/channel.h
index d5eb5d954c0753d3fffb5fb1ad5ba045e5151670..b7b59a447c7ba35e304e7da5025271357c808849 100644
--- a/webrtc/voice_engine/channel.h
+++ b/webrtc/voice_engine/channel.h
@@ -546,6 +546,10 @@ class Channel
 
   const bool use_twcc_plr_for_ana_;
 
+  rtc::CriticalSection encoder_queue_lock_;
+
+  bool encoder_queue_is_active_ GUARDED_BY(encoder_queue_lock_) = false;
+
   rtc::TaskQueue* encoder_queue_ = nullptr;
 };