Make -webkit-font-variant-ligatures actually work.

Right now, the complex text path always ligates, even with
-webkit-font-variant-ligatures:no-common-ligatures. Also, discretionary
and historical ligatures don't work.

This is technically tested by fast/text/font-variant-ligatures.html, but
the default font often doesn't have the GSUB ligature features.
I've changed the test to prefer some fonts that are widely available and
actually have GSUB liga for "fi".

BUG=22240, 114235

Review URL: https://codereview.chromium.org/77413003

git-svn-id: svn://svn.chromium.org/blink/trunk@166751 bbb929c8-8fbe-4397-9dbb-9b2b20218538