Add TRACE_EVENT macros to net.

net/dns/host_cache.cc

Index: net/dns/host_cache.cc
diff --git a/net/dns/host_cache.cc b/net/dns/host_cache.cc
index e38016f159d160cdccd7aff672b6feeed35788b1..4bb2533ba1eef66e3d43f1013793af68252e4a05 100644
--- a/net/dns/host_cache.cc
+++ b/net/dns/host_cache.cc
@@ -8,6 +8,7 @@
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/trace_event/trace_event.h"
 #include "net/base/net_errors.h"
 
 namespace net {
@@ -53,6 +54,7 @@ void HostCache::Set(const Key& key,
                     const Entry& entry,
                     base::TimeTicks now,
                     base::TimeDelta ttl) {
+  TRACE_EVENT0("net", "HostCache::Set");
   DCHECK(CalledOnValidThread());
   if (caching_is_disabled())
     return;