Adjust RtcpReceiver to be testable with callbacks:

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
index ba7ca7e621c5bbebc97980587691ec1ba1a36cdf..78ad5a0ef251386928f3cd9f077126464f159874 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -223,21 +223,7 @@ void ModuleRtpRtcpImpl::SetRtxSendPayloadType(int payload_type,
 int32_t ModuleRtpRtcpImpl::IncomingRtcpPacket(
     const uint8_t* rtcp_packet,
     const size_t length) {
-  // Allow receive of non-compound RTCP packets.
-  RTCPUtility::RTCPParserV2 rtcp_parser(rtcp_packet, length, true);
-
-  const bool valid_rtcpheader = rtcp_parser.IsValid();
-  if (!valid_rtcpheader) {
-    LOG(LS_WARNING) << "Incoming invalid RTCP packet";
-    return -1;
-  }
-  RTCPHelp::RTCPPacketInformation rtcp_packet_information;
-  int32_t ret_val =
-      rtcp_receiver_.IncomingRTCPPacket(rtcp_packet_information, &rtcp_parser);
-  if (ret_val == 0) {
-    rtcp_receiver_.TriggerCallbacksFromRTCPPacket(rtcp_packet_information);
-  }
-  return ret_val;
+  return rtcp_receiver_.IncomingPacket(rtcp_packet, length) ? 0 : -1;
 }
 
 int32_t ModuleRtpRtcpImpl::RegisterSendPayload(