Make FlexfecReceiveStreamImpl::started_ into std::atomic<bool>

webrtc/call/flexfec_receive_stream_impl.h

Index: webrtc/call/flexfec_receive_stream_impl.h
diff --git a/webrtc/call/flexfec_receive_stream_impl.h b/webrtc/call/flexfec_receive_stream_impl.h
index 81c09d6fac79b3c91d2f0ad7f694310bc73d5590..408ffe825f46080d1d5c903554a688402c6ff030 100644
--- a/webrtc/call/flexfec_receive_stream_impl.h
+++ b/webrtc/call/flexfec_receive_stream_impl.h
@@ -11,6 +11,7 @@
 #ifndef WEBRTC_CALL_FLEXFEC_RECEIVE_STREAM_IMPL_H_
 #define WEBRTC_CALL_FLEXFEC_RECEIVE_STREAM_IMPL_H_
 
+#include <atomic>
 #include <memory>
 
 #include "webrtc/call/flexfec_receive_stream.h"
@@ -53,8 +54,7 @@ class FlexfecReceiveStreamImpl : public FlexfecReceiveStream,
  private:
   // Config.
   const Config config_;
-  bool started_ GUARDED_BY(crit_);
-  rtc::CriticalSection crit_;
+  std::atomic<bool> started_;
 
   // Erasure code interfacing.
   const std::unique_ptr<FlexfecReceiver> receiver_;