Add some Retina baselines

Now that the Retina bot is running, we need to generalize some of our
expectations to handle Retina. These changes are only really necessary because
we treat Retina as a version of Mac OS X instead of as a separate configuration
bit. That means MountainLion expectations don't apply to the 10.8 Retina bot.

TBR=dpranke

Review URL: https://codereview.chromium.org/24150003

git-svn-id: svn://svn.chromium.org/blink/trunk@157923 bbb929c8-8fbe-4397-9dbb-9b2b20218538