Move willUseInputColor check to computeInvariantOutput

src/effects/SkDisplacementMapEffect.cpp

Index: src/effects/SkDisplacementMapEffect.cpp
diff --git a/src/effects/SkDisplacementMapEffect.cpp b/src/effects/SkDisplacementMapEffect.cpp
index 59768fc15879ad036998045bbf46daa54068579b..4b01b0f2a09b41a2de6428f0d8fd64e915e8a456 100644
--- a/src/effects/SkDisplacementMapEffect.cpp
+++ b/src/effects/SkDisplacementMapEffect.cpp
@@ -472,7 +472,6 @@ GrDisplacementMapEffect::GrDisplacementMapEffect(
     this->addTextureAccess(&fDisplacementAccess);
     this->addCoordTransform(&fColorTransform);
     this->addTextureAccess(&fColorAccess);
-    this->setWillNotUseInputColor();
 }
 
 GrDisplacementMapEffect::~GrDisplacementMapEffect() {
@@ -498,6 +497,7 @@ void GrDisplacementMapEffect::onComputeInvariantOutput(InvariantOutput* inout) c
     // alpha is 0. Since this isn't trivial to compute at this point, let's assume the output is
     // not of constant color when a displacement effect is applied.
     inout->setToUnknown();
+    inout->setWillNotUseInputColor();
 }
 
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