Distinguish between "flushed" and "finished" idle state callbacks on GrTexture.

This is necessary to convert the promise image API to call Release when all
work is flushed and Done when all work is complete (future work).

Change-Id: I9745952bb0978ca2aaa79aeed460730b2fea856e
Bug: skia:8800
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/197163
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
8 files changed