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 2e6a2c872e5279817cfd3bfbc45b59bb5b0550b8..bc35752c0e824e2f71f02a220c2e67219f0ad962 100644
--- a/src/effects/SkDisplacementMapEffect.cpp
+++ b/src/effects/SkDisplacementMapEffect.cpp
@@ -473,7 +473,6 @@ GrDisplacementMapEffect::GrDisplacementMapEffect(
     this->addTextureAccess(&fDisplacementAccess);
     this->addCoordTransform(&fColorTransform);
     this->addTextureAccess(&fColorAccess);
-    this->setWillNotUseInputColor();
 }
 
 GrDisplacementMapEffect::~GrDisplacementMapEffect() {
@@ -498,7 +497,7 @@ void GrDisplacementMapEffect::onComputeInvariantOutput(InvariantOutput* inout) c
     // and no displacement offset push any texture coordinates out of bounds OR if the constant
     // 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->setToUnknown(InvariantOutput::kWillNot_ReadInput);
 }
 
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