Also add tests for the Noto proprietary fonts. Prior to this commit,
NotoColorEmoji.ttf was unsupported. It's still not well supported, but
the error message returned is now more informative.
Change-Id: I61a3301d7f2458a4b838eb1de7a73d6472e3486f
Reviewed-on: https://go-review.googlesource.com/43694
Reviewed-by: David Crawshaw <crawshaw@golang.org>