Expand modulate, add, subtract, extract component glsl helpers.

src/gpu/gl/GrGLProgram.h

Index: src/gpu/gl/GrGLProgram.h
===================================================================
--- src/gpu/gl/GrGLProgram.h	(revision 8735)
+++ src/gpu/gl/GrGLProgram.h	(working copy)
@@ -125,14 +125,14 @@
      */
     bool genProgram(const GrEffectStage* stages[]);
 
-    void genInputColor(GrGLShaderBuilder* builder, SkString* inColor);
+    GrSLConstantVec genInputColor(GrGLShaderBuilder* builder, SkString* inColor);
 
+    GrSLConstantVec genInputCoverage(GrGLShaderBuilder* builder, SkString* inCoverage);
+
     void genGeometryShader(GrGLShaderBuilder* segments) const;
 
     typedef GrGLUniformManager::UniformHandle UniformHandle;
 
-    void genUniformCoverage(GrGLShaderBuilder* segments, SkString* inOutCoverage);
-
     // Creates a GL program ID, binds shader attributes to GL vertex attrs, and links the program
     bool bindOutputsAttribsAndLinkProgram(const GrGLShaderBuilder& builder,
                                           bool bindColorOut,