Revert "Remove GrDrawingManager::fActiveOpsTask ivar"

This reverts commit f42994335fc78c57bdb45bf6991c404c610ec343.

Reason for revert: Maybe broke Chrome roll?

Original change's description:
> Remove GrDrawingManager::fActiveOpsTask ivar
>
> This thing is just extra state tracking we don't need. Also
> update a couple out-of-date comment blurbs around there.
>
> Bug: skia:10877
> Change-Id: Ibd41afd34d85d52a3d9ebb98e700f5ce9ed3fffb
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/335276
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Commit-Queue: Adlai Holler <adlai@google.com>

TBR=robertphillips@google.com,adlai@google.com

Change-Id: Ia81cb8baa0eca8920dd7489d252e27fbb84818e9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:10877
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/336441
Reviewed-by: Adlai Holler <adlai@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>
4 files changed