Add the internals of RtcEvent's subclasses

webrtc/logging/rtc_event_log/events/rtc_event_audio_playout.cc

 /*
  *  Copyright (c) 2017 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.
  */
 
 #include "webrtc/logging/rtc_event_log/events/rtc_event_audio_playout.h"
 
 namespace webrtc {
 
+RtcEventAudioPlayout::RtcEventAudioPlayout(uint32_t ssrc) : ssrc_(ssrc) {}
+
 RtcEvent::Type RtcEventAudioPlayout::GetType() const {
   return RtcEvent::Type::AudioPlayout;
 }
 
 bool RtcEventAudioPlayout::IsConfigEvent() const {
   return false;
 }
 
 }  // namespace webrtc