Use a direct include of strings headers in remoting/.

remoting/jingle_glue/xmpp_signal_strategy.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 "remoting/jingle_glue/xmpp_signal_strategy.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "base/thread_task_runner_handle.h"
 #include "jingle/glue/chrome_async_socket.h"
 #include "jingle/glue/task_pump.h"
 #include "jingle/glue/xmpp_client_socket_factory.h"
 #include "jingle/notifier/base/gaia_constants.h"
 #include "jingle/notifier/base/gaia_token_pre_xmpp_auth.h"
 #include "net/socket/client_socket_factory.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "third_party/libjingle/source/talk/base/thread.h"
 #include "third_party/libjingle/source/talk/xmpp/prexmppauth.h"
@@ skipping 221 matching lines @@
   std::string mechanism = notifier::kDefaultGaiaAuthMechanism;
   if (settings.token_service() == "oauth2") {
     mechanism = "X-OAUTH2";
   }
 
   return new notifier::GaiaTokenPreXmppAuth(
       jid.Str(), settings.auth_token(), settings.token_service(), mechanism);
 }
 
 }  // namespace remoting