Make metrics const on SkStrike

Change-Id: I13373d7d4f12fec977ad9f77e1b3a9ead91c321d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/254076
Auto-Submit: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
1 file changed