code: func ThrottledReader(
  	ctx context.Context,
  	r io.Reader,
  	throttle Throttle) io.Reader {
  	return &throttledReader{
  		ctx:      ctx,
  		wrapped:  r,
  		throttle: throttle,
  	}
  }
docs: // Create a reader that limits the bandwidth of reads made from r according to
  // the supplied throttler. Reads are assumed to be made under the supplied
  // context.