Express (GLSL expression, possibly known value) pairs as a class

src/gpu/gl/GrGLShaderBuilder.h

Index: src/gpu/gl/GrGLShaderBuilder.h
diff --git a/src/gpu/gl/GrGLShaderBuilder.h b/src/gpu/gl/GrGLShaderBuilder.h
index d73a731a7cd9aaf52d7518d5dfb66413553740b8..a29d73edc40c2e5f42ebb12ff94a26a0d527af53 100644
--- a/src/gpu/gl/GrGLShaderBuilder.h
+++ b/src/gpu/gl/GrGLShaderBuilder.h
@@ -238,18 +238,15 @@ public:
      * TODO: These are used by GrGLProgram to insert a mode color filter. Remove these when the
      * color filter is expressed as a GrEffect.
      */
-    const SkString& getInputColor() const { return fInputColor; }
-    GrSLConstantVec getKnownColorValue() const { return fKnownColorValue; }
-    const SkString& getInputCoverage() const { return fInputCoverage; }
-    GrSLConstantVec getKnownCoverageValue() const { return fKnownCoverageValue; }
+    const GrGLSLExpr<4>& getInputColor() const { return fInputColor; }
+    const GrGLSLExpr<4>& getInputCoverage() const { return fInputCoverage; }
 
     /**
      * Adds code for effects. effectStages contains the effects to add. effectKeys[i] is the key
      * generated from effectStages[i]. An entry in effectStages can be NULL, in which case it is
      * skipped. Moreover, if the corresponding key is GrGLEffect::NoEffectKey then it is skipped.
      * inOutFSColor specifies the input color to the first stage and is updated to be the
-     * output color of the last stage. fsInOutColorKnownValue specifies whether the input color
-     * has a known constant value and is updated to refer to the status of the output color.
+     * output color of the last stage.
      * The handles to texture samplers for effectStage[i] are added to effectSamplerHandles[i]. The
      * glEffects array is updated to contain the GrGLEffect generated for each entry in
      * effectStages.
@@ -257,8 +254,7 @@ public:
     void emitEffects(const GrEffectStage* effectStages[],
                      const GrBackendEffectFactory::EffectKey effectKeys[],
                      int effectCnt,
-                     SkString*  inOutFSColor,
-                     GrSLConstantVec* fsInOutColorKnownValue,
+                     GrGLSLExpr<4>* inOutFSColor,
                      SkTArray<GrGLUniformManager::UniformHandle, true>* effectSamplerHandles[],
                      GrGLEffect* glEffects[]);
 
@@ -476,10 +472,8 @@ private:
     bool                                fSetupFragPosition;
     TextureSampler                      fDstCopySampler;
 
-    SkString                            fInputColor;
-    GrSLConstantVec                     fKnownColorValue;
-    SkString                            fInputCoverage;
-    GrSLConstantVec                     fKnownCoverageValue;
+    GrGLSLExpr<4>                       fInputColor;
+    GrGLSLExpr<4>                       fInputCoverage;
 
     bool                                fHasCustomColorOutput;
     bool                                fHasSecondaryOutput;