Move willUseInputColor check to computeInvariantOutput

src/gpu/effects/GrDitherEffect.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gl/builders/GrGLProgramBuilder.h"
 #include "GrDitherEffect.h"
 
@@ skipping 32 matching lines @@
     virtual bool onIsEqual(const GrFragmentProcessor&) const SK_OVERRIDE { return true; }
 
     virtual void onComputeInvariantOutput(InvariantOutput* inout) const SK_OVERRIDE;
 
     GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
 
     typedef GrFragmentProcessor INHERITED;
 };
 
 void DitherEffect::onComputeInvariantOutput(InvariantOutput* inout) const {
-    inout->setToUnknown();
+    inout->setToUnknown(InvariantOutput::kWill_ReadInput);
 }
 
 //////////////////////////////////////////////////////////////////////////////
 
 GR_DEFINE_FRAGMENT_PROCESSOR_TEST(DitherEffect);
 
 GrFragmentProcessor* DitherEffect::TestCreate(SkRandom*,
                                               GrContext*,
                                               const GrDrawTargetCaps&,
                                               GrTexture*[]) {
@@ skipping 43 matching lines @@
     fsBuilder->codeAppendf("\t\tfloat r = "
                            "fract(sin(dot(%s.xy ,vec2(12.9898,78.233))) * 43758.5453);\n",
                            fsBuilder->fragmentPosition());
     fsBuilder->codeAppendf("\t\t%s = (1.0/255.0) * vec4(r, r, r, r) + %s;\n",
                            outputColor, GrGLSLExpr4(inputColor).c_str());
 }
 
 //////////////////////////////////////////////////////////////////////////////
 
 GrFragmentProcessor* GrDitherEffect::Create() { return DitherEffect::Create(); }