Force clients to specify font when requesting strikecache

Bug: skia:
Change-Id: If56222039239df085d6c40e835060e91fe70940b
Reviewed-on: https://skia-review.googlesource.com/c/173166
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Reed <reed@google.com>
10 files changed