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/rtc_base/nullsocketserver.cc b/rtc_base/nullsocketserver.cc
index c890c6f..ec042dd 100644
--- a/rtc_base/nullsocketserver.cc
+++ b/rtc_base/nullsocketserver.cc
@@ -13,7 +13,7 @@
 
 namespace rtc {
 
-NullSocketServer::NullSocketServer() : event_(false, false) {}
+NullSocketServer::NullSocketServer() = default;
 NullSocketServer::~NullSocketServer() {}
 
 bool NullSocketServer::Wait(int cms, bool process_io) {