Add enterprise policy for network time service

components/network_time/network_time_pref_names.cc

 // Copyright 2014 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/network_time/network_time_pref_names.h"
 
 namespace network_time {
 namespace prefs {
 
 // Stores a pair of local time and corresponding network time to bootstrap
 // network time tracker when browser starts.
 const char kNetworkTimeMapping[] = "network_time.network_time_mapping";
 
+// Stores a boolean indicating whether network time queries should be enabled.
+const char kNetworkTimeQueriesEnabled[] =
+    "network_time.network_time_queries_enabled";
+
 }  // namespace prefs
 }  // namespace network_time