Always use NonBlocking IO for UDP sockets on Windows.

net/socket/datagram_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_DATAGRAM_SOCKET_H_
 #define NET_SOCKET_DATAGRAM_SOCKET_H_
 
 #include "net/base/net_export.h"
 
 namespace net {
@@ skipping 16 matching lines @@
   // Close the socket.
   virtual void Close() = 0;
 
   // Copy the remote udp address into |address| and return a network error code.
   virtual int GetPeerAddress(IPEndPoint* address) const = 0;
 
   // Copy the local udp address into |address| and return a network error code.
   // (similar to getsockname)
   virtual int GetLocalAddress(IPEndPoint* address) const = 0;
 
-  // Switch to use non-blocking IO. Must be called right after construction and
-  // before other calls.
-  virtual void UseNonBlockingIO() = 0;
-
   // Requests that packets sent by this socket not be fragment, either locally
   // by the host, or by routers (via the DF bit in the IPv4 packet header).
   // May not be supported by all platforms. Returns a return a network error
   // code if there was a problem, but the socket will still be usable. Can not
   // return ERR_IO_PENDING.
   virtual int SetDoNotFragment() = 0;
 
   // Gets the NetLog for this socket.
   virtual const NetLogWithSource& NetLog() const = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_SOCKET_DATAGRAM_SOCKET_H_