Mark ~DirectTransport with "override."

webrtc/test/direct_transport.h

Index: webrtc/test/direct_transport.h
diff --git a/webrtc/test/direct_transport.h b/webrtc/test/direct_transport.h
index 32b1fa829c7ee649435f52bf2fad769e8f8aeab6..0698992d5a871f48b266ae718cf11116af0fd3e2 100644
--- a/webrtc/test/direct_transport.h
+++ b/webrtc/test/direct_transport.h
@@ -46,7 +46,7 @@ class DirectTransport : public Transport {
             send_call,
             std::unique_ptr<Demuxer>(new ForceDemuxer(MediaType::VIDEO))) {}
 
-  ~DirectTransport();
+  ~DirectTransport() override;
 
   void SetConfig(const FakeNetworkPipe::Config& config);