Always use NonBlocking IO for UDP sockets on Windows.

net/socket/udp_socket_win.h

Index: net/socket/udp_socket_win.h
diff --git a/net/socket/udp_socket_win.h b/net/socket/udp_socket_win.h
index 9baeb7ba2def47666108f1203b5463fe2f05923a..ce7a8e1585a401bddeff1734b00b488555fec8dc 100644
--- a/net/socket/udp_socket_win.h
+++ b/net/socket/udp_socket_win.h
@@ -197,23 +197,14 @@ class NET_EXPORT UDPSocketWin
   // Resets the thread to be used for thread-safety checks.
   void DetachFromThread();
 
-  // This class by default uses overlapped IO. Call this method before Open()
-  // to switch to non-blocking IO.
-  void UseNonBlockingIO();
-
  private:
   enum SocketOptions {
     SOCKET_OPTION_MULTICAST_LOOP = 1 << 0
   };
 
-  class Core;
-
   void DoReadCallback(int rv);
   void DoWriteCallback(int rv);
 
-  void DidCompleteRead();
-  void DidCompleteWrite();
-
   // base::ObjectWatcher::Delegate implementation.
   void OnObjectSignaled(HANDLE object) override;
   void OnReadSignaled();
@@ -286,14 +277,6 @@ class NET_EXPORT UDPSocketWin
   mutable std::unique_ptr<IPEndPoint> local_address_;
   mutable std::unique_ptr<IPEndPoint> remote_address_;
 
-  // The core of the socket that can live longer than the socket itself. We pass
-  // resources to the Windows async IO functions and we have to make sure that
-  // they are not destroyed while the OS still references them.
-  scoped_refptr<Core> core_;
-
-  // True if non-blocking IO is used.
-  bool use_non_blocking_io_;
-
   // Watches |read_write_event_|.
   base::win::ObjectWatcher read_write_watcher_;