@Override
  @CanIgnoreReturnValue
  public SeekableByteChannel truncate(long size) throws IOException {
    channel.truncate(size);
    return this;
  }
A thin wrapper around a {@link FileChannel} that exists only to implement {@link
SeekableByteChannel} but NOT extend {@link FileChannel}.

@author Colin Decker
jimfs/src/main/java/com/google/common/jimfs/DowngradedSeekableByteChannel.java