Replace two more pairs of {std::unique_ptr} and {size_t} by
{OwnedVector}.

R=mstarzinger@chromium.org

Change-Id: Ifdf03abf9759fbbb4adde76a494073625723a03d
Reviewed-on: https://chromium-review.googlesource.com/1116785
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54057}