Introduce SkGlyphCacheInterface

Change-Id: I54ee9f5a5a13eff0b7f9a07bb22314d8ea2350a4
Reviewed-on: https://skia-review.googlesource.com/148813
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
4 files changed