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

webrtc/base/physicalsocketserver.cc

Index: webrtc/base/physicalsocketserver.cc
diff --git a/webrtc/base/physicalsocketserver.cc b/webrtc/base/physicalsocketserver.cc
index 708499df531f076af2210137c0eb2ed4795c6bab..e2a0b6f14048b4007126ce9a13838f1858fbc1f8 100644
--- a/webrtc/base/physicalsocketserver.cc
+++ b/webrtc/base/physicalsocketserver.cc
@@ -46,6 +46,7 @@
 #include "webrtc/base/common.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/networkmonitor.h"
+#include "webrtc/base/nullsocketserver.h"
 #include "webrtc/base/timeutils.h"
 #include "webrtc/base/winping.h"
 #include "webrtc/base/win32socketinit.h"
@@ -62,6 +63,14 @@ typedef char* SockOptArg;
 
 namespace rtc {
 
+std::unique_ptr<SocketServer> SocketServer::CreateDefault() {
+#if defined(__native_client__)
+  return std::unique_ptr<SocketServer>(new rtc::NullSocketServer);
+#else
+  return std::unique_ptr<SocketServer>(new rtc::PhysicalSocketServer);
+#endif
+}
+
 #if defined(WEBRTC_WIN)
 // Standard MTUs, from RFC 1191
 const uint16_t PACKET_MAXIMUMS[] = {