Replace pooling mechanism with GrMemoryPool.

This change is a wash for tests that could fit inside the previous
hard-coded pool (512 nodes) and appears to be a 5% improvement for
sksl_large. Larger programs would hypothetically show an even more
significant improvement.

When SK_SUPPORT_GPU is disabled, we disable pooling entirely and fall
back to the system allocator. This is necessary because SkSL can exist
without Ganesh (such as in the wasm+CanvasKit build).

Nanobench: http://screen/4xJEzdGducRxGeq

Change-Id: I71dc702a84ab5c163673e35ec651003d7d45dacd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/330219
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
6 files changed