@J2ktIncompatible
  @GwtIncompatible // java serialization not supported in GWT.
  private static byte[] serializeWithBackReference(Object original, int handleOffset)
      throws IOException {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ObjectOutputStream out = new ObjectOutputStream(bos);

    out.writeObject(original);

    byte[] handle = toByteArray(baseWireHandle + handleOffset);

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;