Add GN config for Mac SampleApp

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4077

Change-Id: I67e4456c8ccdb5413e86c442b759f6dff4de651b
Reviewed-on: https://skia-review.googlesource.com/4077
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
5 files changed