Add a SetDoNotFragment() method to DatagramSocket, and call this for

net/udp/udp_socket_posix.h

 // Copyright (c) 2012 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_UDP_UDP_SOCKET_POSIX_H_
 #define NET_UDP_UDP_SOCKET_POSIX_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 101 matching lines @@
              const CompletionCallback& callback);
 
   // Sets the receive buffer size (in bytes) for the socket.
   // Returns a net error code.
   int SetReceiveBufferSize(int32_t size);
 
   // Sets the send buffer size (in bytes) for the socket.
   // Returns a net error code.
   int SetSendBufferSize(int32_t size);
 
+  // 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.
+  int SetDoNotFragment();
+
   // Returns true if the socket is already connected or bound.
   bool is_connected() const { return is_connected_; }
 
   const BoundNetLog& NetLog() const { return net_log_; }
 
   // Sets corresponding flags in |socket_options_| to allow the socket
   // to share the local address to which the socket will be bound with
   // other processes. Should be called between Open() and Bind().
   // Returns a net error code.
   int AllowAddressReuse();
@@ skipping 180 matching lines @@
 
   // Network that this socket is bound to via BindToNetwork().
   NetworkChangeNotifier::NetworkHandle bound_network_;
 
   DISALLOW_COPY_AND_ASSIGN(UDPSocketPosix);
 };
 
 }  // namespace net
 
 #endif  // NET_UDP_UDP_SOCKET_POSIX_H_