Gardening: Widen rebase expectation for fast/text/font-variant-width.html

BUG=419386
TBR=dominik.rottsches@intel.com,eae@chromium.org

Review URL: https://codereview.chromium.org/622173002

git-svn-id: svn://svn.chromium.org/blink/trunk@183165 bbb929c8-8fbe-4397-9dbb-9b2b20218538