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

webrtc/system_wrappers/include/rtp_to_ntp.h

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 23 matching lines @@
                     uint32_t ntp_frac,
                     uint32_t rtp_timestamp,
                     RtcpList* rtcp_list,
                     bool* new_rtcp_sr);
 
 // Converts an RTP timestamp to the NTP domain in milliseconds using two
 // (RTP timestamp, NTP timestamp) pairs.
 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);
 
 }  // namespace webrtc
 
 #endif  // SYSTEM_WRAPPERS_INCLUDE_RTP_TO_NTP_H_