Added [ Mac ] supecifier to the big NeedsRebaseline chuk.

TBR=dcheng
BUG=

Review URL: https://codereview.chromium.org/21518002

git-svn-id: svn://svn.chromium.org/blink/trunk@155325 bbb929c8-8fbe-4397-9dbb-9b2b20218538