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

net/udp/udp_socket_win.cc

 // 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.
 
 #include "net/udp/udp_socket_win.h"
 
 #include <mstcpip.h>
 
 #include "base/callback.h"
 #include "base/lazy_instance.h"
@@ skipping 520 matching lines @@
                   reinterpret_cast<char*>(&actual_size), &option_size);
   if (rv != 0)
     return MapSystemError(WSAGetLastError());
   if (actual_size >= size)
     return OK;
   UMA_HISTOGRAM_CUSTOM_COUNTS("Net.SocketUnchangeableSendBuffer",
                               actual_size, 1000, 1000000, 50);
   return ERR_SOCKET_SEND_BUFFER_SIZE_UNCHANGEABLE;
 }
 
+int UDPSocketWin::SetDoNotFragment() {
+  DCHECK_NE(socket_, INVALID_SOCKET);
+  DCHECK(CalledOnValidThread());
+
+  if (addr_family_ == AF_INET6)
+    return OK;
+
+  DWORD val = 1;
+  int rv = setsockopt(socket_, IPPROTO_IP, IP_DONTFRAGMENT,
+                      reinterpret_cast<const char*>(&val), sizeof(val));
+  return rv == 0 ? OK : MapSystemError(WSAGetLastError());
+}
+
 int UDPSocketWin::AllowAddressReuse() {
   DCHECK_NE(socket_, INVALID_SOCKET);
   DCHECK(CalledOnValidThread());
   DCHECK(!is_connected());
 
   BOOL true_value = TRUE;
   int rv = setsockopt(socket_, SOL_SOCKET, SO_REUSEADDR,
                       reinterpret_cast<const char*>(&true_value),
                       sizeof(true_value));
   return rv == 0 ? OK : MapSystemError(WSAGetLastError());
@@ skipping 624 matching lines @@
 void UDPSocketWin::DetachFromThread() {
   base::NonThreadSafe::DetachFromThread();
 }
 
 void UDPSocketWin::UseNonBlockingIO() {
   DCHECK(!core_);
   use_non_blocking_io_ = true;
 }
 
 }  // namespace net