[FastTextAutosizer] Enable the non-flaky hackernews-comments.html test

hackernews-comments.html was marked as flaky in crbug.com/343201 but
no longer appears to be flaky. This is likely from our recent
improvements in this area.

BUG=343201
TBR=skobes
NOTRY=true

Review URL: https://codereview.chromium.org/238983004

git-svn-id: svn://svn.chromium.org/blink/trunk@171674 bbb929c8-8fbe-4397-9dbb-9b2b20218538