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);
 
+  // Configures the socket to set or clear the DF (Do not Fragment) bit on

[Jeremy Dorfman, 2016/08/12 17:23:41]

This can't clear the DF bit now. Also, for IPv6, it prevents hosts from
fragmenting them -- routers aren't allowed to fragment IPv6 packets.

[Ryan Hamilton, 2016/08/12 17:40:53]

Done.

+  // packets, which prevents routers from fragmenting them.
+  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_