In GrOpFlushState, store GrOp* rather than Unique ID

This makes the comment on GrOp::uniqeID (that it's only used for audit
trail) true again. More importantly, it avoids always cycling through op
IDs, which can actually overflow. This makes Draw slightly bigger, but
saves the atomic overhead of getting a new ID for each op. Both of those
are probably too small to measure.

Bug: skia:8575
Change-Id: I6aecf0c72b85c59e8644a4574ccbeeb71997baca
Reviewed-on: https://skia-review.googlesource.com/c/173423
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed