Use the WebKit default fonts when specifying generic font families.

This pipes through a new preferences object that the font system can use.
It now picks up these faces as well as the default font size.

Clarify this behavior in the interface.

TEST=manual (font example included).
BUG=none
Review URL: http://codereview.chromium.org/7053022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@86870 0039d316-1c4b-4281-b951-d872f2087c98
21 files changed