GrBufferAllocPool: use _throw calloc() if unchecked.

Looks like this code is using sk_calloc(), NULL on failure, accidentally
instead of sk_calloc_throw().  We're using sk_malloc_throw() in the parallel
code path, so it really seems like we're not checking the result pointer.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2152753002

Review-Url: https://codereview.chromium.org/2152753002
1 file changed