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

net/socket/unix_domain_client_socket_posix.h

 // Copyright 2014 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_UNIX_DOMAIN_CLIENT_SOCKET_POSIX_H_
 #define NET_SOCKET_UNIX_DOMAIN_CLIENT_SOCKET_POSIX_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 51 matching lines @@
 
   // Socket implementation.
   int Read(IOBuffer* buf,
            int buf_len,
            const CompletionCallback& callback) override;
   int Write(IOBuffer* buf,
             int buf_len,
             const CompletionCallback& callback) override;
   int SetReceiveBufferSize(int32_t size) override;
   int SetSendBufferSize(int32_t size) override;
+  int SetDoNotFragment(bool do_not_fragment) override;
 
   // Releases ownership of underlying SocketDescriptor to caller.
   // Internal state is reset so that this object can be used again.
   // Socket must be connected in order to release it.
   SocketDescriptor ReleaseConnectedSocket();
 
  private:
   const std::string socket_path_;
   const bool use_abstract_namespace_;
   std::unique_ptr<SocketPosix> socket_;
   // This net log is just to comply StreamSocket::NetLog(). It throws away
   // everything.
   BoundNetLog net_log_;
 
   DISALLOW_COPY_AND_ASSIGN(UnixDomainClientSocket);
 };
 
 }  // namespace net
 
 #endif  // NET_SOCKET_UNIX_DOMAIN_CLIENT_SOCKET_POSIX_H_