Add a test for font/line-height cascade.

The line-height property has lots of special handling in the style
resolver which we want to remove at some point. When we do, it's nice to
know that this still works correctly.

R=rune@opera.com
BUG=353932

Review URL: https://codereview.chromium.org/678483005

git-svn-id: svn://svn.chromium.org/blink/trunk@184346 bbb929c8-8fbe-4397-9dbb-9b2b20218538