Add the internals of RtcEvent's subclasses

webrtc/logging/rtc_event_log/events/rtc_event_logging_started.h

 /*
  *  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.
  */
 
 #ifndef WEBRTC_LOGGING_RTC_EVENT_LOG_EVENTS_RTC_EVENT_LOGGING_STARTED_H_
 #define WEBRTC_LOGGING_RTC_EVENT_LOG_EVENTS_RTC_EVENT_LOGGING_STARTED_H_
 
 #include "webrtc/logging/rtc_event_log/events/rtc_event.h"
+#include "webrtc/typedefs.h"
 
 namespace webrtc {
 
 class RtcEventLoggingStarted final : public RtcEvent {
  public:
+  explicit RtcEventLoggingStarted(int64_t timestamp_us);
   ~RtcEventLoggingStarted() override = default;
 
   Type GetType() const override;
+
+  int64_t timestamp_us_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_LOGGING_RTC_EVENT_LOG_EVENTS_RTC_EVENT_LOGGING_STARTED_H_