Fix TSAN race in webrtc::voe::Channel

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 2be86be5aa5af91c58e54d71533762236cb0c256..25a27c3236aac4609b51b610403232d45832bee7 100644
--- a/webrtc/voice_engine/channel.h
+++ b/webrtc/voice_engine/channel.h
@@ -416,7 +416,7 @@ class Channel
                                 RTPExtensionType type,
                                 unsigned char id);
 
-  void UpdateOverheadForEncoder();
+  void UpdateOverheadForEncoder(size_t overhead_per_packet);

[hta-webrtc, 2017/02/28 12:21:20]

Should there be a lock notation here saying "must be called with
overhead_per_packet_lock held"?

It's private, so I guess it's OK to leave it out.

[hbos, 2017/02/28 12:32:53]

Good idea! There's EXCLUSIVE_LOCKS_REQUIRED. Now using that, which also meant I
could remove the function parameter and calculate it inside of the function
instead knowing the lock is already held.

 
   int GetRtpTimestampRateHz() const;
   int64_t GetRTT(bool allow_associate_channel) const;
@@ -497,8 +497,9 @@ class Channel
   uint32_t _lastLocalTimeStamp;
   int8_t _lastPayloadType;
   bool _includeAudioLevelIndication;
-  size_t transport_overhead_per_packet_;
-  size_t rtp_overhead_per_packet_;
+  size_t transport_overhead_per_packet_ GUARDED_BY(overhead_per_packet_lock_);
+  size_t rtp_overhead_per_packet_ GUARDED_BY(overhead_per_packet_lock_);
+  rtc::CriticalSection overhead_per_packet_lock_;
   // VoENetwork
   AudioFrame::SpeechType _outputSpeechType;
   // VoEVideoSync