Introduce GenericFontFamilySettings.

The newborn will hold all settings, related to generic font
families, and will be used by Settings.

Aside from mechanical extraction, there is one functional change:
setting font families will require explicit call to recalc style
on all frames. Thankfully, this is already done in most places,
aside from InternalSettings, where I added it.

R=eae,ksakamoto@chromium.org
BUG=324991

Review URL: https://codereview.chromium.org/100653002

git-svn-id: svn://svn.chromium.org/blink/trunk@163117 bbb929c8-8fbe-4397-9dbb-9b2b20218538