Get known hashes from GS directly

Bug: skia:
Change-Id: I8698aad706e2c9cc81280107cb08d83e08a9dc25
Reviewed-on: https://skia-review.googlesource.com/18145
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Stephan Altmueller <stephana@google.com>
37 files changed