Add TRACE_EVENT macros to net.

net/udp/udp_socket_posix.cc

Index: net/udp/udp_socket_posix.cc
diff --git a/net/udp/udp_socket_posix.cc b/net/udp/udp_socket_posix.cc
index 331bb7757e4a136b3038a0114a963d28a2cf3d72..7e75b860574bb7f3af3ca8f8f88f4d101b383c29 100644
--- a/net/udp/udp_socket_posix.cc
+++ b/net/udp/udp_socket_posix.cc
@@ -20,6 +20,7 @@
 #include "base/metrics/sparse_histogram.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/rand_util.h"
+#include "base/trace_event/trace_event.h"
 #include "net/base/io_buffer.h"
 #include "net/base/ip_address.h"
 #include "net/base/ip_endpoint.h"
@@ -413,6 +414,8 @@ int UDPSocketPosix::SetBroadcast(bool broadcast) {
 }
 
 void UDPSocketPosix::ReadWatcher::OnFileCanReadWithoutBlocking(int) {
+  TRACE_EVENT0("net",
+               "UDPSocketPosix::ReadWatcher::OnFileCanReadWithoutBlocking");
   if (!socket_->read_callback_.is_null())
     socket_->DidCompleteRead();
 }