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 8ac2c43e9a220e0c814e9d8fcf12bc66c313909d..6fe85745c3bb72974253b527e1804530269b262e 100644
--- a/webrtc/video/receive_statistics_proxy.cc
+++ b/webrtc/video/receive_statistics_proxy.cc
@@ -78,8 +78,11 @@ ReceiveStatisticsProxy::ReceiveStatisticsProxy(
       avg_rtt_ms_(0),
       frame_window_accumulated_bytes_(0) {
   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() {