Standardize "net" category trace events

net/log/trace_constants.cc

Index: net/log/trace_constants.cc
diff --git a/net/log/trace_constants.cc b/net/log/trace_constants.cc
new file mode 100644
index 0000000000000000000000000000000000000000..2566cfc6e0a4c39245f651bbfd213b50df9d7b31
--- /dev/null
+++ b/net/log/trace_constants.cc
@@ -0,0 +1,13 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/log/trace_constants.h"
+
+#include "base/trace_event/common/trace_event_common.h"
+
+namespace net {
+
+const char kNetTracingCategory[] = TRACE_DISABLED_BY_DEFAULT("net");
+
+}  // namespace net