Reland "Inset blur domain a tiny bit to prevent certain GPUs from sampling transparent black from scratch textures."
Reland "Inset blur domain a tiny bit to prevent certain GPUs from sampling transparent black from scratch textures."

This is a reland of 730c53ae3c81736dc1877a5d520700a767ea2f7a

Original change's description:
> Inset blur domain a tiny bit to prevent certain GPUs from sampling transparent black from scratch textures.
> 
> When running Skia GPU blur on an iPhone X, I noticed a bit a of transparency seeping into my clamped blur on the right and/or bottom edges of certain-sized rectangular blurs with large blur radii.
> 
> I could only repro this on an iPhone X; I couldn't repro on a retina Macbook Pro or a 1x external screen.
> 
> I think the iPhone X GPU is rounding the sampling coordinate a little differently than most other GPUs or there's some floating point error involved in the shader that makes it sample pixels outside of the desired blur domain. Since the blur source is inside a scratch texture filled with transparent black, some undesirable transparent black gets pulled in when we're decimating and blurring the source.
> 
> Bug: https://bugs.chromium.org/p/skia/issues/detail?id=8942
> 
> Change-Id: Iff28c3ee5d069c6999a831d4b156a650be3a9eb8
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/205208
> Reviewed-by: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>
> Commit-Queue: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>

Bug: https://bugs.chromium.org/p/skia/issues/detail?id=8942
Change-Id: Id7737476e36ab824d5e50b8d7c3c8a7468a7807b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/205821
Reviewed-by: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>
Commit-Queue: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>

rubenvb/skia,google/skia,google/skia,HalCanary/skia-hc,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,rubenvb/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,aosp-mirror/platform_external_skia,rubenvb/skia,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,rubenvb/skia,rubenvb/skia,google/skia,HalCanary/skia-hc,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,rubenvb/skia,google/skia,aosp-mirror/platform_external_skia,rubenvb/skia,rubenvb/skia,rubenvb/skia,rubenvb/skia