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

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

This reverts commit db3ceb86421fb9da86bb920e3a1f0957beec08d9.

Reason for revert: observing some strange budget behavior w/ instrumented Chromium builds;  need to investigate.

Original change's description:
> 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>
>

TBR=bsalomon@google.com,robertphillips@google.com,fmalita@chromium.org,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I8ca9862ad1519a9ec69ad1ce8e4d129b0dae7b0a
Reviewed-on: https://skia-review.googlesource.com/9524
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>