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

webrtc/base/socketserver.h

 /*
  *  Copyright 2004 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.
  */
 
 #ifndef WEBRTC_BASE_SOCKETSERVER_H_
 #define WEBRTC_BASE_SOCKETSERVER_H_
 
+#include <memory>
 #include "webrtc/base/socketfactory.h"
 
 namespace rtc {
 
 class MessageQueue;
 class NetworkBinderInterface;
 
 // Provides the ability to wait for activity on a set of sockets.  The Thread
 // class provides a nice wrapper on a socket server.
 //
 // The server is also a socket factory.  The sockets it creates will be
 // notified of asynchronous I/O from this server's Wait method.
 class SocketServer : public SocketFactory {
  public:
   static const int kForever = -1;
 
+  static std::unique_ptr<SocketServer> CreateDefault();
   // When the socket server is installed into a Thread, this function is
   // called to allow the socket server to use the thread's message queue for
   // any messaging that it might need to perform.
   virtual void SetMessageQueue(MessageQueue* queue) {}
 
   // Sleeps until:
   //  1) cms milliseconds have elapsed (unless cms == kForever)
   //  2) WakeUp() is called
   // While sleeping, I/O is performed if process_io is true.
   virtual bool Wait(int cms, bool process_io) = 0;
 
   // Causes the current wait (if one is in progress) to wake up.
   virtual void WakeUp() = 0;
 
   // A network binder will bind the created sockets to a network.
   // It is only used in PhysicalSocketServer.
   void set_network_binder(NetworkBinderInterface* binder) {
     network_binder_ = binder;
   }
   NetworkBinderInterface* network_binder() const { return network_binder_; }
 
  private:
   NetworkBinderInterface* network_binder_ = nullptr;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_SOCKETSERVER_H_