Don't use color type derived from GrPixelConfig to determine proxy texture swizzle.

Change-Id: Ib19e378d7dd8243cbbee68e97bcb3b6159943500
Bug: skia:6718
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/233898
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/effects/generated/GrRRectBlurEffect.h b/src/gpu/effects/generated/GrRRectBlurEffect.h
index aa00554..ffec0a3 100644
--- a/src/gpu/effects/generated/GrRRectBlurEffect.h
+++ b/src/gpu/effects/generated/GrRRectBlurEffect.h
@@ -51,8 +51,8 @@
 
         GrProxyProvider* proxyProvider = context->priv().proxyProvider();
 
-        sk_sp<GrTextureProxy> mask(
-                proxyProvider->findOrCreateProxyByUniqueKey(key, kBottomLeft_GrSurfaceOrigin));
+        sk_sp<GrTextureProxy> mask(proxyProvider->findOrCreateProxyByUniqueKey(
+                key, GrColorType::kAlpha_8, kBottomLeft_GrSurfaceOrigin));
         if (!mask) {
             // TODO: this could be approx but the texture coords will need to be updated
             sk_sp<GrRenderTargetContext> rtc(