Add text autosizing testcase for the hackernews comment issue

This patch adds a testcase for autosizing comments on hackernews
(news.ycombinator.com). This has traditionally been a tough case for
autosizing implementations and we would like to catch progressions in
this case.

TBR=skobes
BUG=302005

Review URL: https://codereview.chromium.org/25722005

git-svn-id: svn://svn.chromium.org/blink/trunk@158763 bbb929c8-8fbe-4397-9dbb-9b2b20218538