public synchronized void addPrivateChunk(String type, byte[] data) {
        chunkType.add(type);
        chunkData.add(data.clone());
    }
Adds a private chunk, in binary form, to the list of chunks to
be stored with this image.

@param type a 4-character String giving the chunk type name.
@param data an array of <code>byte</code>s containing the
       chunk data.
plugins/svg-plugin/batik-codec-fix/src/main/java/org/apache/batik/ext/awt/image/codec/png/PNGEncodeParam.java