Create helper functions to use in computeInvariantOutput calls

src/effects/SkLightingImageFilter.cpp

 /*
  * Copyright 2012 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkLightingImageFilter.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
@@ skipping 337 matching lines @@
 
     const SkLight* light() const { return fLight; }
     SkScalar surfaceScale() const { return fSurfaceScale; }
     const SkMatrix& filterMatrix() const { return fFilterMatrix; }
 
 protected:
     virtual bool onIsEqual(const GrProcessor&) const SK_OVERRIDE;
 
     virtual void onComputeInvariantOutput(InvariantOutput* inout) const SK_OVERRIDE {
         // lighting shaders are complicated. We just throw up our hands.
-        inout->fValidFlags = 0;
-        inout->fIsSingleComponent = false;
+        inout->mulByUnknownColor();
     }
 
 private:
     typedef GrSingleTextureEffect INHERITED;
     const SkLight* fLight;
     SkScalar fSurfaceScale;
     SkMatrix fFilterMatrix;
 };
 
 class GrDiffuseLightingEffect : public GrLightingEffect {
@@ skipping 1349 matching lines @@
 
     fsBuilder->codeAppendf("%s(%s)", fLightColorFunc.c_str(), surfaceToLight);
 }
 
 #endif
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkLightingImageFilter)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkDiffuseLightingImageFilter)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkSpecularLightingImageFilter)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END