Mac GN doc.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3906
NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=3906

Change-Id: I1ad13dd5b7df3d76f99f11e02f04169c5b37ce95
Reviewed-on: https://skia-review.googlesource.com/3906
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed