Fix a bug in run-webkit-tests where a test is expected to fail, fails differently and then passes on a retry.

We would, confusingly, report this as a regression even though it really is
more of an unexpected pass (or even, arguably, a flake).

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/113453009

git-svn-id: svn://svn.chromium.org/blink/trunk@164204 bbb929c8-8fbe-4397-9dbb-9b2b20218538