Cleanup size calculations in SkGlyph

BUG=skia:7515

Change-Id: Ie9d255a93ecff86ce018f8510332bdb280ec575e
Reviewed-on: https://skia-review.googlesource.com/113863
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
5 files changed