Add event traces to interesting places in WebRTC.

Bug: webrtc:12840
Change-Id: I2fe749039059c9f3d6da064dce10d9c24a27d02e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/221044
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34199}

call/rtp_video_sender.cc

diff --git a/call/rtp_video_sender.cc b/call/rtp_video_sender.cc
index c2a6a56..110e28b 100644
--- a/call/rtp_video_sender.cc
+++ b/call/rtp_video_sender.cc
@@ -31,6 +31,7 @@
 #include "rtc_base/location.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/task_queue.h"
+#include "rtc_base/trace_event.h"
 
 namespace webrtc {
 
@@ -461,6 +462,7 @@
 
 void RtpVideoSender::RegisterProcessThread(
     ProcessThread* module_process_thread) {
+  TRACE_EVENT0("webrtc", "RtpVideoSender::RegisterProcessThread");
   RTC_DCHECK_RUN_ON(&module_process_thread_checker_);
   RTC_DCHECK(!module_process_thread_);
   module_process_thread_ = module_process_thread;