Add default constructor for rtc::Event

Bug: webrtc:9962
Change-Id: Icaa91e657e6881fcb1553f354c07866109a0ea68
Reviewed-on: https://webrtc-review.googlesource.com/c/109500
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25535}
diff --git a/audio/channel_send.cc b/audio/channel_send.cc
index cc8b1f7..c0de939 100644
--- a/audio/channel_send.cc
+++ b/audio/channel_send.cc
@@ -595,7 +595,7 @@
   // to acccess and invalid channel object.
   RTC_DCHECK(encoder_queue_);
 
-  rtc::Event flush(false, false);
+  rtc::Event flush;
   {
     // Clear |encoder_queue_is_active_| under lock to prevent any other tasks
     // than this final "flush task" to be posted on the queue.