da90c53e was incorrect; the size()
functions take almost anything, not just word characters, and
std::extent() uses brackets.

BUG=837308

Change-Id: I6ee75a5da7a021758bbfb0996aeaef81f2003cd9
Reviewed-on: https://chromium-review.googlesource.com/c/1401581Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>