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 dc3351120c89d458222e715ad0a872f5804dc2c7..716baa398095da0618f03d0c2a7b2423c914fbac 100644
--- a/webrtc/logging/rtc_event_log/rtc_event_log.h
+++ b/webrtc/logging/rtc_event_log/rtc_event_log.h
@@ -97,12 +97,12 @@ 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);
   }