SkGlyphCache - update core routines.

- Allows different methods for creating SkGlyphCaches
- Enables passing FontMetrics for cache creation.
- Removes VisitCache
- Removes VisitAll
- Introduces SkExclusiveStrikePtr which should
  replaces SkAutoGlyphCache with simpler mechanism.

BUG=skia:7515

Change-Id: Ibada35e3985335179d2cc8284a837fc525224c92
Reviewed-on: https://skia-review.googlesource.com/111063
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
5 files changed