Split FontDataCache out of FontCache.

Get gFontDataCache logic outta FontCache and into its own nice class.

I also grouped other caches into static funcs in preparation for
splitting them off, too.

R=eae,ksakamoto@chromium.org
BUG=315783

Review URL: https://codereview.chromium.org/84773005

git-svn-id: svn://svn.chromium.org/blink/trunk@162674 bbb929c8-8fbe-4397-9dbb-9b2b20218538