Add ClearCache() {} to the non-caching case.
This is a reland of cfdae5a56c
Original change's description:
> remove the OpMemoryPool
>
> Change-Id: I987384f8009445ba8308e85b75daf4880a8d36be
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/383957
> Reviewed-by: Michael Ludwig <michaelludwig@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Herb Derby <herb@google.com>
Change-Id: I03f80ba61f5643c40f812a9687b12a5d2aa663b1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/385276
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
3230255e06