NFC: clang-format rL374420 and adjust comment wording

The commit of rL374420 had various formatting issues, including lines
that exceed 80 columns. This patch applies `git clang-format` on the
changes from commit 13bd3ef4.

It further adjusts a comment to clarify the domain of inputs upon which
a newly added function is meant to operate. The adjustment to the
comment was suggested in a post-commit comment on D68721 and discussed
off-list with @sfertile.

llvm-svn: 374635