Add TRACE_EVENT macros to net.

net/url_request/url_fetcher_core.cc

Index: net/url_request/url_fetcher_core.cc
diff --git a/net/url_request/url_fetcher_core.cc b/net/url_request/url_fetcher_core.cc
index ee1a3d8c83010938d4c6d10cedc3e69fd348384b..213884f71b8d859a15f382af84fa3e061f1a39b5 100644
--- a/net/url_request/url_fetcher_core.cc
+++ b/net/url_request/url_fetcher_core.cc
@@ -15,6 +15,7 @@
 #include "base/single_thread_task_runner.h"
 #include "base/stl_util.h"
 #include "base/thread_task_runner_handle.h"
+#include "base/trace_event/trace_event.h"
 #include "base/tracked_objects.h"
 #include "net/base/elements_upload_data_stream.h"
 #include "net/base/io_buffer.h"
@@ -514,6 +515,7 @@ URLFetcherCore::~URLFetcherCore() {
 }
 
 void URLFetcherCore::StartOnIOThread() {
+  TRACE_EVENT0("net", "URLFetcherCore::StartOnIOThread");
   DCHECK(network_task_runner_->BelongsToCurrentThread());
 
   if (!response_writer_)
@@ -746,6 +748,7 @@ void URLFetcherCore::DidFinishWriting(int result) {
 }
 
 void URLFetcherCore::RetryOrCompleteUrlFetch() {
+  TRACE_EVENT0("net", "URLFetcherCore::RetryOrCompleteUrlFetch");
   DCHECK(network_task_runner_->BelongsToCurrentThread());
   base::TimeDelta backoff_delay;