Pack WebCore::Font slightly better

From WebKit r152689 by Andreas Kling <akling@apple.com>

Knock 8 bytes off of Font by packing the members better. Reduces memory consumption by 429 kB when viewing the full HTML5 spec at <http://whatwg.org/c>.

Review URL: https://chromiumcodereview.appspot.com/19278010

git-svn-id: svn://svn.chromium.org/blink/trunk@154339 bbb929c8-8fbe-4397-9dbb-9b2b20218538