Standardize "net" category trace events

net/socket/udp_socket_posix.cc

Index: net/socket/udp_socket_posix.cc
diff --git a/net/socket/udp_socket_posix.cc b/net/socket/udp_socket_posix.cc
index 8b8c227ebc83e191a0600a95d522ba14669c8f85..10b6762e554bef51c3bfa2262125c49d0b59c0b1 100644
--- a/net/socket/udp_socket_posix.cc
+++ b/net/socket/udp_socket_posix.cc
@@ -27,6 +27,7 @@
 #include "net/base/net_errors.h"
 #include "net/base/network_activity_monitor.h"
 #include "net/base/sockaddr_storage.h"
+#include "net/base/trace_constants.h"
 #include "net/log/net_log.h"
 #include "net/log/net_log_event_type.h"
 #include "net/log/net_log_source.h"
@@ -574,7 +575,7 @@ int UDPSocketPosix::SetBroadcast(bool broadcast) {
 }
 
 void UDPSocketPosix::ReadWatcher::OnFileCanReadWithoutBlocking(int) {
-  TRACE_EVENT0("net",
+  TRACE_EVENT0(kNetTracingCategory,
                "UDPSocketPosix::ReadWatcher::OnFileCanReadWithoutBlocking");
   if (!socket_->read_callback_.is_null())
     socket_->DidCompleteRead();