Add STSubRunAllocator, an inline SubRunAllocator

Bug: oss-fuzz:48695
Bug: oss-fuzz:48690
Change-Id: I9fb634df54f8e1e7dee84036e2be2512d7a395d8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/556030
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed