[NOT FOR REVIEW] Instrument net/ with trace events.

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 ea1a560289e3700187a53075f2a1cef7c9479c0e..10f29a0509826233acecf8d83755cddf89339d0b 100644
--- a/net/udp/udp_socket_posix.cc
+++ b/net/udp/udp_socket_posix.cc
@@ -29,6 +29,8 @@
 #include "net/socket/socket_descriptor.h"
 #include "net/udp/udp_net_log_parameters.h"
 
+#include "base/trace_event/trace_event.h"
+
 #if defined(OS_ANDROID)
 #include "base/android/build_info.h"
 #include "base/native_library.h"
@@ -412,6 +414,8 @@ int UDPSocketPosix::SetBroadcast(bool broadcast) {
 }
 
 void UDPSocketPosix::ReadWatcher::OnFileCanReadWithoutBlocking(int) {
+  TRACE_EVENT0(
+      "net", "net::UDPSocketPosix::ReadWatcher::OnFileCanReadWithoutBlocking");
   if (!socket_->read_callback_.is_null())
     socket_->DidCompleteRead();
 }