Adds clearer function to create rtc::Thread without Physical SocketServer

webrtc/base/BUILD.gn

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build/config/crypto.gni")
 import("//build/config/ui.gni")
@@ skipping 256 matching lines @@
     "messagehandler.cc",
     "messagehandler.h",
     "messagequeue.cc",
     "messagequeue.h",
     "nethelpers.cc",
     "nethelpers.h",
     "network.cc",
     "network.h",
     "networkmonitor.cc",
     "networkmonitor.h",
+    "nullsocketserver.cc",
     "nullsocketserver.h",
     "openssl.h",
     "openssladapter.cc",
     "openssladapter.h",
     "openssldigest.cc",
     "openssldigest.h",
     "opensslidentity.cc",
     "opensslidentity.h",
     "opensslstreamadapter.cc",
     "opensslstreamadapter.h",
@@ skipping 346 matching lines @@
       ]
     }
   }
 }
 
 source_set("gtest_prod") {
   sources = [
     "gtest_prod_util.h",
   ]
 }