Make RtcEventLogImpl to use a TaskQueue instead of a helper-thread

webrtc/logging/rtc_event_log/rtc_event_log.h

 /*
  *  Copyright (c) 2015 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.
  */
 
@@ skipping 80 matching lines @@
   // e.g. because we are already logging or the file cannot be opened.
   virtual bool StartLogging(const std::string& file_name,
                             int64_t max_size_bytes) = 0;
 
   // Same as above. The RtcEventLog takes ownership of the file if the call
   // is successful, i.e. if it returns true.
   virtual bool StartLogging(rtc::PlatformFile platform_file,
                             int64_t max_size_bytes) = 0;
 
   // Deprecated. Pass an explicit file size limit.
-  bool StartLogging(const std::string& file_name) {
+  RTC_DEPRECATED bool StartLogging(const std::string& file_name) {
     return StartLogging(file_name, 10000000);
   }
 
   // Deprecated. Pass an explicit file size limit.
-  bool StartLogging(rtc::PlatformFile platform_file) {
+  RTC_DEPRECATED bool StartLogging(rtc::PlatformFile platform_file) {
     return StartLogging(platform_file, 10000000);
   }
 
-  // Stops logging to file and waits until the thread has finished.
+  // Stops logging to file and waits until the file has been closed, after
+  // which it would be permissible to read and/or modify it.
   virtual void StopLogging() = 0;
 
   // Logs configuration information for a video receive stream.
   virtual void LogVideoReceiveStreamConfig(
       const rtclog::StreamConfig& config) = 0;
 
   // Logs configuration information for a video send stream.
   virtual void LogVideoSendStreamConfig(const rtclog::StreamConfig& config) = 0;
 
   // Logs configuration information for an audio receive stream.
@@ skipping 102 matching lines @@
                               int min_probes,
                               int min_bytes) override{};
   void LogProbeResultSuccess(int id, int bitrate_bps) override{};
   void LogProbeResultFailure(int id,
                              ProbeFailureReason failure_reason) override{};
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_LOGGING_RTC_EVENT_LOG_RTC_EVENT_LOG_H_