Use a direct include of strings headers in chromeos/.

chromeos/network/network_change_notifier_chromeos.cc

 // Copyright (c) 2012 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 <string>
 
 #include "base/basictypes.h"
 #include "base/bind.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/network/network_change_notifier_chromeos.h"
 #include "chromeos/network/network_state.h"
 #include "chromeos/network/network_state_handler.h"
 #include "net/base/network_change_notifier.h"
 #include "net/dns/dns_config_service_posix.h"
 #include "third_party/cros_system_api/dbus/service_constants.h"
 
 namespace chromeos {
 
@@ skipping 189 matching lines @@
   // produce a single signal when switching between network connections.
   params.ip_address_offline_delay_ = base::TimeDelta::FromMilliseconds(4000);
   params.ip_address_online_delay_ = base::TimeDelta::FromMilliseconds(1000);
   params.connection_type_offline_delay_ =
       base::TimeDelta::FromMilliseconds(500);
   params.connection_type_online_delay_ = base::TimeDelta::FromMilliseconds(500);
   return params;
 }
 
 }  // namespace chromeos