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

webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc

Index: webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc
diff --git a/webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc b/webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc
index 5ba3353f43cb60112ac6d0b6419273a9d41a9e16..f9f9fb71928f876de15f32092c7aa2549b348cde 100644
--- a/webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc
+++ b/webrtc/system_wrappers/source/rtp_to_ntp_unittest.cc
@@ -150,6 +150,23 @@ TEST(RtpToNtpTests, FailsForDecreasingRtpTimestamp) {
   EXPECT_FALSE(RtpToNtpMs(kTimestamp1, rtcp, &timestamp_in_ms));
 }
 
+TEST(RtpToNtpTests, RtpToNtpMsWithReturnedFrequency) {
+  const uint32_t kNtpSec1 = 3683354930;
+  const uint32_t kNtpFrac1 = 699925050;
+  const uint32_t kTimestamp1 = 2192705742;
+  const uint32_t kNtpSec2 = kNtpSec1;
+  const uint32_t kNtpFrac2 = kNtpFrac1 + kOneMsInNtpFrac;
+  const uint32_t kTimestamp2 = kTimestamp1 + kTimestampTicksPerMs;
+  RtcpList rtcp;
+  rtcp.push_front(RtcpMeasurement(kNtpSec1, kNtpFrac1, kTimestamp1));
+  rtcp.push_front(RtcpMeasurement(kNtpSec2, kNtpFrac2, kTimestamp2));
+  int64_t timestamp_in_ms;
+  double freq_khz;
+  EXPECT_TRUE(
+      RtpToNtpMsAndReturnFreq(kTimestamp1, rtcp, &timestamp_in_ms, &freq_khz));
+  EXPECT_DOUBLE_EQ(90.0, freq_khz);
+}
+
 TEST(UpdateRtcpListTests, InjectRtcpSrWithEqualNtp) {
   RtcpList rtcp;
   uint32_t ntp_sec = 0;