Hold sk_sp<GrAtlasTextBlob> refs in GrTextBlobCache instead of raw ptrs

Refactor to store sk_sps, and minimize explicit ref manipulation.

Change-Id: Ie3d18e5fe1cefbbc5c2f3c4941287a24038522a6
Reviewed-on: https://skia-review.googlesource.com/9490
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
6 files changed