public static <T> int mergeDelimitedFrom(DataInput in, T message, Schema<T> schema)
            throws IOException
    {
        return IOUtil.mergeDelimitedFrom(in, message, schema, false);
    }
Used by the code generated messages that implement {@link java.io.Externalizable}. Merges from the
{@link DataInput}.

@return the size of the message
protostuff-core/src/main/java/io/protostuff/ProtobufIOUtil.java