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

webrtc/base/socketserver.h

Index: webrtc/base/socketserver.h
diff --git a/webrtc/base/socketserver.h b/webrtc/base/socketserver.h
index 1b4136d74e3246010ac770f13d5baf2337bc8307..7071f2252687c9b4e31471bb1f0af0ef9f326672 100644
--- a/webrtc/base/socketserver.h
+++ b/webrtc/base/socketserver.h
@@ -11,6 +11,7 @@
 #ifndef WEBRTC_BASE_SOCKETSERVER_H_
 #define WEBRTC_BASE_SOCKETSERVER_H_
 
+#include <memory>
 #include "webrtc/base/socketfactory.h"
 
 namespace rtc {
@@ -27,6 +28,7 @@ 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.