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

net/udp/udp_socket_win.h

Index: net/udp/udp_socket_win.h
diff --git a/net/udp/udp_socket_win.h b/net/udp/udp_socket_win.h
index 14b801e36fe4d44e3f807f3464424a95e146656f..97f2de6bba4af550ab28c0a83e47f715b90dcd58 100644
--- a/net/udp/udp_socket_win.h
+++ b/net/udp/udp_socket_win.h
@@ -124,6 +124,13 @@ class NET_EXPORT UDPSocketWin
   // Returns a net error code.
   int SetSendBufferSize(int32_t size);
 
+  // Configures the socket to set the DF (Do not Fragment) bit on packets,
+  // which prevents routers from fragmenting them. Also, for IPv6, it
+  // prevents hosts from fragmenting them. 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_; }