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

net/udp/datagram_socket.h

Index: net/udp/datagram_socket.h
diff --git a/net/udp/datagram_socket.h b/net/udp/datagram_socket.h
index f0e9fa10baa7fb181b9b2cc6810459c6c31359d6..0562a8aa9efb9f1243afb69e939c4882831f082b 100644
--- a/net/udp/datagram_socket.h
+++ b/net/udp/datagram_socket.h
@@ -34,6 +34,13 @@ class NET_EXPORT_PRIVATE DatagramSocket {
   // (similar to getsockname)
   virtual int GetLocalAddress(IPEndPoint* address) const = 0;
 
+  // If supported by the platform, 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.
+  virtual int SetDoNotFragment() = 0;
+
   // Gets the NetLog for this socket.
   virtual const BoundNetLog& NetLog() const = 0;
 };