Convert rtc_event_log from webrtc::Clock to rtc::TimeMicros.

webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h

Index: webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h
diff --git a/webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h b/webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h
index bda27f2f4ffb17f7139618ece923314a58688b4c..7d41f60db22c6f67806d9f98a0245ef04e94e2dc 100644
--- a/webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h
+++ b/webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h
@@ -23,7 +23,6 @@
 #include "webrtc/base/platform_thread.h"
 #include "webrtc/base/swap_queue.h"
 #include "webrtc/logging/rtc_event_log/ringbuffer.h"
-#include "webrtc/system_wrappers/include/clock.h"
 #include "webrtc/system_wrappers/include/file_wrapper.h"
 
 #ifdef ENABLE_RTC_EVENT_LOG
@@ -69,8 +68,7 @@ class RtcEventLogHelperThread final {
 
   RtcEventLogHelperThread(
       SwapQueue<ControlMessage>* message_queue,
-      SwapQueue<std::unique_ptr<rtclog::Event>>* event_queue,
-      const Clock* const clock);
+      SwapQueue<std::unique_ptr<rtclog::Event>>* event_queue);
   ~RtcEventLogHelperThread();
 
   // This function MUST be called once a STOP_FILE message is added to the
@@ -120,8 +118,6 @@ class RtcEventLogHelperThread final {
   rtc::Event wake_from_hibernation_;
   rtc::Event file_finished_;
 
-  const Clock* const clock_;
-
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(RtcEventLogHelperThread);
 };