API to cache shader binaries between runs of Skia.

This CL does not include an actual implementation of said cache.
Stan is working on the cache implementation on the Android side of
things.

Bug: skia:
Change-Id: Iabe4f19b2dbacaaa1ead8bb3fa68d88c687b9a84
Reviewed-on: https://skia-review.googlesource.com/54780
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
19 files changed