Mute font rendering LayoutTest that are asserting in harfbuzz

TBR=eseidel
NOTRY=true
NOTREECHECKS=true

Review URL: https://codereview.chromium.org/640273002

git-svn-id: svn://svn.chromium.org/blink/trunk@183474 bbb929c8-8fbe-4397-9dbb-9b2b20218538