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

net/udp/udp_socket_win.cc

Index: net/udp/udp_socket_win.cc
diff --git a/net/udp/udp_socket_win.cc b/net/udp/udp_socket_win.cc
index 42cb05af9d24bc6aace1f09918d9881ffdfc8666..b8c3b5831a346be6cbdf0587b4604ce389676f2f 100644
--- a/net/udp/udp_socket_win.cc
+++ b/net/udp/udp_socket_win.cc
@@ -538,6 +538,19 @@ int UDPSocketWin::SetSendBufferSize(int32_t size) {
   return ERR_SOCKET_SEND_BUFFER_SIZE_UNCHANGEABLE;
 }
 
+int UDPSocketWin::SetDoNotFragment() {
+  DCHECK_NE(socket_, INVALID_SOCKET);
+  DCHECK(CalledOnValidThread());
+
+  if (addr_family_ == AF_INET6)
+    return OK;
+
+  DWORD val = 1;
+  int rv = setsockopt(socket_, IPPROTO_IP, IP_DONTFRAGMENT,
+                      reinterpret_cast<const char*>(&val), sizeof(val));
+  return rv == 0 ? OK : MapSystemError(WSAGetLastError());
+}
+
 int UDPSocketWin::AllowAddressReuse() {
   DCHECK_NE(socket_, INVALID_SOCKET);
   DCHECK(CalledOnValidThread());