Add Mac 10.8 (retina) builder to garden-o-matic.
Add Mac 10.8 (retina) builder to garden-o-matic.

R=abarth@chromium.org, ojan@chromium.org
BUG=292886

Review URL: https://chromiumcodereview.appspot.com/23681013

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@157871 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs