make run-webkit-tests --chromium --lint-test-files work properly

We were taking 'chromium' as the actual name of a port in lint_test_expectations.py and not matching anything.

R=ojan@chromium.org
BUG=242673

Review URL: https://codereview.chromium.org/17395007

git-svn-id: svn://svn.chromium.org/blink/trunk@152965 bbb929c8-8fbe-4397-9dbb-9b2b20218538