Revert "Make FP optimizations helpers use SkAlphaType not GrColorType"

This reverts commit 7a538b1eeccdbe940de507af9aeaf454952c4aec.

Reason for revert: ios failures

Original change's description:
> Make FP optimizations helpers use SkAlphaType not GrColorType
> 
> Change-Id: I3b7cde6e7f68192af5419fb09c7d59e7a803a4d5
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255818
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Greg Daniel <egdaniel@google.com>

TBR=egdaniel@google.com,bsalomon@google.com

Change-Id: Id41daa47fb3ccac434bb9d71a697f32e36c87367
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255835
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp b/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
index 59bc8ce..fd70616 100644
--- a/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
+++ b/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
@@ -211,15 +211,16 @@
 }
 
 GrGaussianConvolutionFragmentProcessor::GrGaussianConvolutionFragmentProcessor(
-        sk_sp<GrTextureProxy> proxy,
-        SkAlphaType alphaType,
-        Direction direction,
-        int radius,
-        float gaussianSigma,
-        GrTextureDomain::Mode mode,
-        int bounds[2])
+                                                            sk_sp<GrTextureProxy> proxy,
+                                                            GrColorType srcColorType,
+                                                            Direction direction,
+                                                            int radius,
+                                                            float gaussianSigma,
+                                                            GrTextureDomain::Mode mode,
+                                                            int bounds[2])
         : INHERITED(kGrGaussianConvolutionFragmentProcessor_ClassID,
-                    ModulateForSamplerOptFlags(alphaType, mode == GrTextureDomain::kDecal_Mode))
+                    ModulateForSamplerOptFlags(srcColorType,
+                                               mode == GrTextureDomain::kDecal_Mode))
         , fCoordTransform(proxy.get())
         , fTextureSampler(std::move(proxy))
         , fRadius(radius)
@@ -297,9 +298,8 @@
     int radius = d->fRandom->nextRangeU(1, kMaxKernelRadius);
     float sigma = radius / 3.f;
 
-    auto alphaType = static_cast<SkAlphaType>(d->fRandom->nextULessThan(kLastEnum_SkAlphaType + 1));
     return GrGaussianConvolutionFragmentProcessor::Make(
-            std::move(proxy), alphaType, dir, radius, sigma,
-            static_cast<GrTextureDomain::Mode>(modeIdx), bounds);
+            std::move(proxy), d->textureProxyColorType(texIdx),
+            dir, radius, sigma, static_cast<GrTextureDomain::Mode>(modeIdx), bounds);
 }
 #endif