Add stats for frequency offset when converting RTP timestamp to NTP time.

webrtc/system_wrappers/source/rtp_to_ntp.cc

Index: webrtc/system_wrappers/source/rtp_to_ntp.cc
diff --git a/webrtc/system_wrappers/source/rtp_to_ntp.cc b/webrtc/system_wrappers/source/rtp_to_ntp.cc
index 05091461d4123ff9bfbea041bd18187a0c411e02..5bca4c094a3bba2cc889c8206130b928846e5222 100644
--- a/webrtc/system_wrappers/source/rtp_to_ntp.cc
+++ b/webrtc/system_wrappers/source/rtp_to_ntp.cc
@@ -96,6 +96,15 @@ bool UpdateRtcpList(uint32_t ntp_secs,
 bool RtpToNtpMs(int64_t rtp_timestamp,
                 const RtcpList& rtcp,
                 int64_t* rtp_timestamp_in_ms) {
+  double frequency_khz;
+  return RtpToNtpMsAndReturnFreq(rtp_timestamp, rtcp, rtp_timestamp_in_ms,
+                                 &frequency_khz);
+}
+
+bool RtpToNtpMsAndReturnFreq(int64_t rtp_timestamp,

[stefan-webrtc, 2016/10/05 14:35:46]

Instead of introducing this slightly odd function, could we instead split it up
in two?

bool GetRtpToNtpParameters(const RtcpList& rtcp, double*
estimated_frequency_khz, double* estimated_offset)

and 

bool RtpToNtpMs(int64_t rtp_timestamp, double rtp_frequency, double offset,
int64_t* rtp_timestamp_in_ms)

[åsapersson, 2016/10/09 14:22:15]

The old timestamp in the RctpList is used in RtpToNtpMs to check for wrap
around. I updated the cl so the parameters are calculated when the rtcp list is
updated, ptal. 

+                             const RtcpList& rtcp,
+                             int64_t* rtp_timestamp_in_ms,
+                             double* estimated_frequency_khz) {
   if (rtcp.size() != 2)
     return false;
 
@@ -133,6 +142,7 @@ bool RtpToNtpMs(int64_t rtp_timestamp,
     return false;
   }
   *rtp_timestamp_in_ms = rtp_timestamp_ntp_ms;
+  *estimated_frequency_khz = freq_khz;
   return true;
 }