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

webrtc/system_wrappers/include/rtp_to_ntp.h

Index: webrtc/system_wrappers/include/rtp_to_ntp.h
diff --git a/webrtc/system_wrappers/include/rtp_to_ntp.h b/webrtc/system_wrappers/include/rtp_to_ntp.h
index 0c91928626dd8701599c0744f3a046661126cb76..727b61154e66bb294b94a138e503f75fb3352715 100644
--- a/webrtc/system_wrappers/include/rtp_to_ntp.h
+++ b/webrtc/system_wrappers/include/rtp_to_ntp.h
@@ -41,6 +41,12 @@ bool UpdateRtcpList(uint32_t ntp_secs,
 bool RtpToNtpMs(int64_t rtp_timestamp, const RtcpList& rtcp,
                 int64_t* timestamp_in_ms);
 
+// Same as above and returns the frequency used in the conversion.
+bool RtpToNtpMsAndReturnFreq(int64_t rtp_timestamp,
+                             const RtcpList& rtcp,
+                             int64_t* timestamp_in_ms,
+                             double* estimated_frequency_khz);
+
 // Returns 1 there has been a forward wrap around, 0 if there has been no wrap
 // around and -1 if there has been a backwards wrap around (i.e. reordering).
 int CheckForWrapArounds(uint32_t rtp_timestamp, uint32_t rtcp_rtp_timestamp);