Revert "remove fAllocators from GrOpsTask"

This reverts commit f00d6a8efd723ecccda716d0360df49bdc48feaa.

Reason for revert: In the long run, it seems like this might leak.

Original change's description:
> remove fAllocators from GrOpsTask
>
> Change-Id: I5901f005c2758a92692e5cd70ba46a2b5ad797fd
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/393116
> Commit-Queue: Herb Derby <herb@google.com>
> Reviewed-by: Adlai Holler <adlai@google.com>
> Reviewed-by: Chris Dalton <csmartdalton@google.com>
> Reviewed-by: Robert Phillips <robertphillips@google.com>

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

Change-Id: I895e47c999c6961fa14c356d6d5bde80dd86b63e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/393176
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
3 files changed