gn format: don't break+indent if it's going to be forced past 80col anyway

A penalty is accrued for each character past 80col, but when both
breaking and not breaking are too long, don't break because it doesn't
help readability.

R=brettw@chromium.org,dpranke@chromium.org
BUG=348474

Review URL: https://codereview.chromium.org/775793003

Cr-Original-Commit-Position: refs/heads/master@{#306515}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 5cd14553570320fa95a467cdd4f2fdd42945b73f