Revert "Rename chromium-mac* ports to mac*"

This reverts commit b28ff57057ff78be6b24f8eaee9c04a9f11db374.

This change broke the Mac layout bots, as they explicitly pass
'--platform chromium-mac' to run_webkit_tests.py.

BUG=231188
TBR=ojan

Review URL: https://codereview.chromium.org/18293002

git-svn-id: svn://svn.chromium.org/blink/trunk@153310 bbb929c8-8fbe-4397-9dbb-9b2b20218538