Potentially optimize some GrGLEffects for known input color values

src/effects/SkColorMatrixFilter.cpp

Index: src/effects/SkColorMatrixFilter.cpp
diff --git a/src/effects/SkColorMatrixFilter.cpp b/src/effects/SkColorMatrixFilter.cpp
index 1e3c779ec661d36e1e8e4aca12acdc769b9555b7..2228855984fa52cc579316ec8b185b386f9c1f6b 100644
--- a/src/effects/SkColorMatrixFilter.cpp
+++ b/src/effects/SkColorMatrixFilter.cpp
@@ -398,7 +398,7 @@ public:
                               const GrDrawEffect&,
                               EffectKey,
                               const char* outputColor,
-                              const char* inputColor,
+                              const GrGLSLExpr4& inputColor,
                               const TransformedCoordsArray&,
                               const TextureSamplerArray&) SK_OVERRIDE {
             fMatrixHandle = builder->addUniform(GrGLShaderBuilder::kFragment_Visibility,
@@ -408,17 +408,13 @@ public:
                                                 kVec4f_GrSLType,
                                                 "ColorMatrixVector");
 
-            if (NULL == inputColor) {
-                // could optimize this case, but we aren't for now.
-                inputColor = "vec4(1)";
-            }
             // The max() is to guard against 0 / 0 during unpremul when the incoming color is
             // transparent black.
-            builder->fsCodeAppendf("\tfloat nonZeroAlpha = max(%s.a, 0.00001);\n", inputColor);
+            builder->fsCodeAppendf("\tfloat nonZeroAlpha = %s;\n", GrGLSL::max(inputColor.a(), 0.00001f).c_str());
             builder->fsCodeAppendf("\t%s = %s * vec4(%s.rgb / nonZeroAlpha, nonZeroAlpha) + %s;\n",
                                    outputColor,
                                    builder->getUniformCStr(fMatrixHandle),
-                                   inputColor,
+                                   inputColor.c_str(),
                                    builder->getUniformCStr(fVectorHandle));
             builder->fsCodeAppendf("\t%s.rgb *= %s.a;\n", outputColor, outputColor);
         }