Modify webkit-patch rebaseline-expectations to work on win.

R=pkasting@chromium.org
BUG=396362

Review URL: https://codereview.chromium.org/407373002

git-svn-id: svn://svn.chromium.org/blink/trunk@178729 bbb929c8-8fbe-4397-9dbb-9b2b20218538