Use NullSocketServer instead of PhysicalSocketServer in SignalThread

webrtc/base/nethelpers.cc

 /*
  *  Copyright 2008 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.
  */
 
@@ skipping 64 matching lines @@
         addresses->push_back(ip);
       }
     }
   }
   freeaddrinfo(result);
   return 0;
 #endif  // !__native_client__
 }
 
 // AsyncResolver
-AsyncResolver::AsyncResolver() : error_(-1) {
-}
+AsyncResolver::AsyncResolver()
+    : SignalThread(false /* use_socket_server */), error_(-1) {}
 
 AsyncResolver::~AsyncResolver() = default;
 
 void AsyncResolver::Start(const SocketAddress& addr) {
   addr_ = addr;
   // SignalThred Start will kickoff the resolve process.
   SignalThread::Start();
 }
 
 bool AsyncResolver::GetResolvedAddress(int family, SocketAddress* addr) const {
@@ skipping 92 matching lines @@
       break;
     }
   }
   freeifaddrs(ifa);
   return has_ipv6;
 #else
   return true;
 #endif
 }
 }  // namespace rtc