add fontmetrics to SkFont

Bug: skia:2664
Change-Id: I49030b6010e08814ec50c75dd26b44a5265d74bd
Reviewed-on: https://skia-review.googlesource.com/c/167461
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
12 files changed