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

webrtc/logging/rtc_event_log/rtc_event_log.h

Index: webrtc/logging/rtc_event_log/rtc_event_log.h
diff --git a/webrtc/logging/rtc_event_log/rtc_event_log.h b/webrtc/logging/rtc_event_log/rtc_event_log.h
index d26dccbea96b2058521f31dd083753171639e861..087f5d9b77a3cad2d3ba0124f78d049ac5d4efa2 100644
--- a/webrtc/logging/rtc_event_log/rtc_event_log.h
+++ b/webrtc/logging/rtc_event_log/rtc_event_log.h
@@ -98,16 +98,17 @@ class RtcEventLog {
                             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.