Potentially optimize some GrGLEffects for known input color values

src/effects/SkMatrixConvolutionImageFilter.cpp

Index: src/effects/SkMatrixConvolutionImageFilter.cpp
diff --git a/src/effects/SkMatrixConvolutionImageFilter.cpp b/src/effects/SkMatrixConvolutionImageFilter.cpp
index 8e703b6b40900bcb5e2c6b9a9962e44752bdcc71..9ec7185b6e1e835784f0d618a7a4dbaa36d8ca47 100644
--- a/src/effects/SkMatrixConvolutionImageFilter.cpp
+++ b/src/effects/SkMatrixConvolutionImageFilter.cpp
@@ -324,7 +324,7 @@ public:
                           const GrDrawEffect&,
                           EffectKey,
                           const char* outputColor,
-                          const char* inputColor,
+                          const GrGLSLExpr4& inputColor,
                           const TransformedCoordsArray&,
                           const TextureSamplerArray&) SK_OVERRIDE;
 
@@ -382,7 +382,7 @@ void GrGLMatrixConvolutionEffect::emitCode(GrGLShaderBuilder* builder,
                                            const GrDrawEffect&,
                                            EffectKey key,
                                            const char* outputColor,
-                                           const char* inputColor,
+                                           const GrGLSLExpr4& inputColor,
                                            const TransformedCoordsArray& coords,
                                            const TextureSamplerArray& samplers) {
     sk_ignore_unused_variable(inputColor);