Reorganize strike cache and glyph cache code

BUG=skia:7515

Change-Id: I05867890e88de7a7d23b60d9eec989d93d39d333
Reviewed-on: https://skia-review.googlesource.com/121783
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
6 files changed