Revert "Disable resource cache in shadow_utils GM for now"

Revert "Disable resource cache in shadow_utils GM for now"

This reverts commit c34a946d5a975ba8b8cd51f79b55174a5ec0f99f.

Reason for revert: This is probably fixed with https://skia-review.googlesource.com/c/17279/.

Original change's description:
> Disable resource cache in shadow_utils GM for now
>
> This should make the GMs more stable in tiled mode.
>
> Change-Id: I72996b1305fc99e60626af35267952d0a5c38624
> Reviewed-on: https://skia-review.googlesource.com/17275
> Reviewed-by: Mike Reed <reed@google.com>
> Commit-Queue: Jim Van Verth <jvanverth@google.com>
>

TBR=jvanverth@google.com,reed@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I0d21652a301b3f81e7ec04638bedbaabc723e583
Reviewed-on: https://skia-review.googlesource.com/17304
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>