virtual/antialiasedtext/fast/text/emphasis-combined-text.html constantly fails

See: http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=virtual%2Fantialiasedtext%2Ffast%2Ftext%2Femphasis-combined-text.html

BUG=418884
TBR=zmo@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/617733002

git-svn-id: svn://svn.chromium.org/blink/trunk@182891 bbb929c8-8fbe-4397-9dbb-9b2b20218538