Move tracked prefs into services/preferences/tracked.

components/user_prefs/tracked/pref_names.cc

Index: components/user_prefs/tracked/pref_names.cc
diff --git a/components/user_prefs/tracked/pref_names.cc b/components/user_prefs/tracked/pref_names.cc
deleted file mode 100644
index a6c73a65228769269481706d175c8e4edd3d98d0..0000000000000000000000000000000000000000
--- a/components/user_prefs/tracked/pref_names.cc
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright 2015 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 "components/user_prefs/tracked/pref_names.h"
-
-namespace user_prefs {
-
-// A timestamp (stored in base::Time::ToInternalValue format) of the last time
-// a preference was reset.
-const char kPreferenceResetTime[] = "prefs.preference_reset_time";
-
-}  // namespace user_prefs