Move GrBlobSubRun into GrSubRun

Start moving to a single set of SubRuns by unifying the
Blob and the SubRun interfaces. GrSubRun will contain the
API for Blobs.

Change-Id: I0bb8eb2c8f62d243d1b158fcaf94b3bcac37f315
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/533982
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed