Update invariant output computation for various texture effects.

src/gpu/effects/GrCustomCoordsTextureEffect.cpp

Index: src/gpu/effects/GrCustomCoordsTextureEffect.cpp
diff --git a/src/gpu/effects/GrCustomCoordsTextureEffect.cpp b/src/gpu/effects/GrCustomCoordsTextureEffect.cpp
index 39f44820b0013b79443d5bb0e37d64b06eda6207..f61a37bb6fbed860aa0fc97657007d61890ffd3d 100644
--- a/src/gpu/effects/GrCustomCoordsTextureEffect.cpp
+++ b/src/gpu/effects/GrCustomCoordsTextureEffect.cpp
@@ -68,7 +68,9 @@ bool GrCustomCoordsTextureEffect::onIsEqual(const GrGeometryProcessor& other) co
 }
 
 void GrCustomCoordsTextureEffect::onComputeInvariantOutput(GrInvariantOutput* inout) const {
-    if (GrPixelConfigIsOpaque(this->texture(0)->config())) {
+    if (GrPixelConfigIsAlphaOnly(this->texture(0)->config())) {
+        inout->mulByUnknownAlpha();
+    } else if (GrPixelConfigIsOpaque(this->texture(0)->config())) {
         inout->mulByUnknownOpaqueColor();
     } else {
         inout->mulByUnknownColor();