This initially supports reading two common system fonts. At some point there should be a more general Open function, but first I need to work out how to to turn font names into android file names. Fixes golang/go#9419. Change-Id: I8321df873315a5222c39dccf961f742f2e2a7a4c Reviewed-on: https://go-review.googlesource.com/2059 Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>