Add ramp-up tests for transport sequence number with and w/o audio.

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 444ab26fcb052387c2445e1b0c1a1bda360ba54d..d68bc7184ebc45e7619002aa906ff530b2026cc9 100644
--- a/webrtc/test/direct_transport.h
+++ b/webrtc/test/direct_transport.h
@@ -46,6 +46,8 @@ class DirectTransport : public Transport {
                const PacketOptions& options) override;
   bool SendRtcp(const uint8_t* data, size_t length) override;
 
+  int GetAverageDelayMs();
+
  private:
   static bool NetworkProcess(void* transport);
   bool SendPackets();