Make -webkit-font-kerning actually work.

Right now, the complex text path always kerns, even with
-webkit-font-kerning:none.

This is technically tested by fast/text/font-kerning.html, but the default font
often only has TrueType kerning, which isn't supported yet (bug 41990).
I've changed the test to prefer some fonts that are widely available and
actually get kerned.

BUG=165643

Review URL: https://codereview.chromium.org/74413002

git-svn-id: svn://svn.chromium.org/blink/trunk@162485 bbb929c8-8fbe-4397-9dbb-9b2b20218538