Fix NeedsRebaseline to ImageOnlyFailure in TestExpectations.

Because a ref test cannot be marked NeedsRebaseline.

TBR=mvanouwerkerk@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/135683005

git-svn-id: svn://svn.chromium.org/blink/trunk@165772 bbb929c8-8fbe-4397-9dbb-9b2b20218538