Revert "Don't dither const shaders that don't have a GP override"
Revert "Don't dither const shaders that don't have a GP override"

This reverts commit 05a4b12dbdf279280c691be0ccf31b718bde10c7.

Reason for revert: Speculative fix for b/220676062

Original change's description:
> Don't dither const shaders that don't have a GP override
>
> https://gold.skia.org/detail?test=gradients_no_texture&digest=008c796df4da7fbb6718e96db2c36c90
>
> If paintFP was only non-null because it came from the main SkShader, we
> should defer to SkPaintPriv's check that the shader is not a constant.
> We don't have a isConstant() for FPs so this assumes that if the GP
> overrides it with a new FP it probably is doing something spatially
> interesting and does need the dithering.
>
> Bug: skia:12516
> Change-Id: I7935ba8f0baf91e7b7ba07280452871c60ffd3e8
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/509996
> Commit-Queue: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>
> Auto-Submit: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>
> Reviewed-by: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
> Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>

Bug: skia:12516
Change-Id: I9c45f457d42cd5890cc110617e1636ffa6669503
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/511808
Reviewed-by: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>

aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia