Rename various methods in webkitpy.layout_test.Port to be public

They were misleadingly named w/ leading underscores as if they were private.

R=scottmg@chromium.org
BUG=30536

Review URL: https://codereview.chromium.org/150573014

git-svn-id: svn://svn.chromium.org/blink/trunk@166692 bbb929c8-8fbe-4397-9dbb-9b2b20218538