Reland "Add memsets to the GrBlockAllocator unit tests."

This is a reland of 87bc83eaa6988d34b123013f4af79ef261599574

Original change's description:
> Add memsets to the GrBlockAllocator unit tests.
>
> These will verify that our blocks are actually set up properly--if not,
> we'll stomp over a sentinel word and/or trip an ASAN poisoned byte,
> causing the test to fail.
>
> Change-Id: I2dcb5b913d00c408f70c71f2660c6ec6017b452c
> Bug: skia:10885
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/332260
> Reviewed-by: Michael Ludwig <michaelludwig@google.com>
> Commit-Queue: Michael Ludwig <michaelludwig@google.com>
> Auto-Submit: John Stiles <johnstiles@google.com>

Bug: skia:10885
Change-Id: Ie1ffcfeffec14a016b50e6464fc23878b4dd2ccb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/332716
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
1 file changed