Remove private inheritance

It doesn't seem to have point.

Bug: None
Change-Id: I5e8131578c1191be9f0c27a5196425669470319c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626920
Commit-Queue: Sang Woo Ko <sangwoo108@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662944}
1 file changed