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

net/udp/udp_socket_posix.h

Index: net/udp/udp_socket_posix.h
diff --git a/net/udp/udp_socket_posix.h b/net/udp/udp_socket_posix.h
index 305c435334ae0c4f27de4f29b72b66671a92207a..b6f4f4b30a7826ae41e2630f93432e5850947487 100644
--- a/net/udp/udp_socket_posix.h
+++ b/net/udp/udp_socket_posix.h
@@ -119,6 +119,13 @@ class NET_EXPORT UDPSocketPosix : public base::NonThreadSafe {
   // 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_; }