Reland of Make RTX pt/apt reconfigurable by calling WebRtcVideoChannel2::SetRecvParameters.

webrtc/video/receive_statistics_proxy.cc

Index: webrtc/video/receive_statistics_proxy.cc
diff --git a/webrtc/video/receive_statistics_proxy.cc b/webrtc/video/receive_statistics_proxy.cc
index 68050ba6a8a440dcc3eb31a4edf22127d99949c0..ba9184a2d4a7a7d2c8c9ed8800d185a8d49716f4 100644
--- a/webrtc/video/receive_statistics_proxy.cc
+++ b/webrtc/video/receive_statistics_proxy.cc
@@ -71,8 +71,11 @@ ReceiveStatisticsProxy::ReceiveStatisticsProxy(
       freq_offset_counter_(clock, nullptr, kFreqOffsetProcessIntervalMs),
       first_report_block_time_ms_(-1) {
   stats_.ssrc = config_.rtp.remote_ssrc;
-  for (auto it : config_.rtp.rtx)
-    rtx_stats_[it.second.ssrc] = StreamDataCounters();
+  // TODO(brandtr): Replace |rtx_stats_| with a single instance of
+  // StreamDataCounters.
+  if (config_.rtp.rtx_ssrc) {
+    rtx_stats_[config_.rtp.rtx_ssrc] = StreamDataCounters();
+  }
 }
 
 ReceiveStatisticsProxy::~ReceiveStatisticsProxy() {