Use the RTT from RtcpRttStats class if provided when sending/receiving NACK.

R=holmer@google.com

Review URL: https://webrtc-codereview.appspot.com/5049004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5228 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.h

@@ -405,6 +405,7 @@ class ModuleRtpRtcpImpl : public RtpRtcp {
   Clock*                    clock_;
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(RtpRtcpImplTest, Rtt);
   FRIEND_TEST_ALL_PREFIXES(RtpRtcpImplTest, RttForReceiverOnly);
   int64_t RtcpReportInterval();
   void SetRtcpReceiverSsrcs(uint32_t main_ssrc);