Always use NonBlocking IO for UDP sockets on Windows.

net/socket/udp_client_socket.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_SOCKET_UDP_CLIENT_SOCKET_H_
 #define NET_SOCKET_UDP_CLIENT_SOCKET_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 24 matching lines @@
   NetworkChangeNotifier::NetworkHandle GetBoundNetwork() const override;
   int Read(IOBuffer* buf,
            int buf_len,
            const CompletionCallback& callback) override;
   int Write(IOBuffer* buf,
             int buf_len,
             const CompletionCallback& callback) override;
   void Close() override;
   int GetPeerAddress(IPEndPoint* address) const override;
   int GetLocalAddress(IPEndPoint* address) const override;
-  void UseNonBlockingIO() override;
   int SetReceiveBufferSize(int32_t size) override;
   int SetSendBufferSize(int32_t size) override;
   int SetDoNotFragment() override;
   const NetLogWithSource& NetLog() const override;
 
   // Switch to use non-blocking IO. Must be called right after construction and
   // before other calls.
  private:
   UDPSocket socket_;
   NetworkChangeNotifier::NetworkHandle network_;
   DISALLOW_COPY_AND_ASSIGN(UDPClientSocket);
 };
 
 }  // namespace net
 
 #endif  // NET_SOCKET_UDP_CLIENT_SOCKET_H_