A safe Slug/TextBlob + alloc allocator

Change-Id: I4799eb0f6d1c00c220509eadfa16fcb6fabdeebc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/536105
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
5 files changed