Consider [0, 1] with the Lebesgue measure.
Is there any sequence ${f_n}$ of nonnegative integrable functions defined on [0, 1] such that $f_n$ converges to 0 in measure, but the sequence ${g_n}$ defined by $g_n =\frac{f_1 + \cdots + f_n}{n}$ does not converge to 0 in measure?