Recently git cl format has started requiring GN and would fail when run
in the ANGLE standalone repository because the binary was not present.

BUG=

Change-Id: I0482db6fd6a868dc02ef6e395e6ff4817623c291
Reviewed-on: https://chromium-review.googlesource.com/326420Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>