re2: merge 6569a9a

This was accidentally the GitHub main branch head for a while,
and now Chromium refers to it. Merge it into the history so that
Chromium checkouts can advance past it.

It was committed to Gerrit as bf6416b instead.

Change-Id: I285f069f6f3a00bc836e35bbc9ea1b8f2ed3f921

Author: rsc