code: func ProfileSample(w io.Writer, r io.Reader, res time.Duration) (pw io.Writer, pr io.Reader, done func() SamplingProfile) {
  	return profileSample(clock.New(), w, r, res)
  }
docs: // ProfileSample will wrap a writer and reader pair and collect
  // samples of where time is spent: writing or reading. The result
  // is an approximation that is returned when the `done` func is
  // called. The `done` func can be called *only once*.
  //
  // This call is not as precise as the `Profile` call, but the
  // performance overhead is much reduced.