Add SkSourceGammaTreatment enum so we know how to create mips

src/core/SkComposeShader.cpp

Index: src/core/SkComposeShader.cpp
diff --git a/src/core/SkComposeShader.cpp b/src/core/SkComposeShader.cpp
index 46b7724944676a297b5745b4f658ec40dd34ca5c..25c9edd611d1b185587cac3635db86f4ddc8a1eb 100644
--- a/src/core/SkComposeShader.cpp
+++ b/src/core/SkComposeShader.cpp
@@ -186,7 +186,8 @@ void SkComposeShader::ComposeShaderContext::shadeSpan(int x, int y, SkPMColor re
 const GrFragmentProcessor* SkComposeShader::asFragmentProcessor(GrContext* context,
                                                             const SkMatrix& viewM,
                                                             const SkMatrix* localMatrix,
-                                                            SkFilterQuality fq) const {
+                                                            SkFilterQuality fq,
+                                                            bool gammaCorrect) const {
     // Fragment processor will only support SkXfermode::Mode modes currently.
     SkXfermode::Mode mode;
     if (!(SkXfermode::AsMode(fMode, &mode))) {
@@ -199,19 +200,19 @@ const GrFragmentProcessor* SkComposeShader::asFragmentProcessor(GrContext* conte
                                                  GrConstColorProcessor::kIgnore_InputMode);
             break;
         case SkXfermode::kSrc_Mode:
-            return fShaderB->asFragmentProcessor(context, viewM, localMatrix, fq);
+            return fShaderB->asFragmentProcessor(context, viewM, localMatrix, fq, gammaCorrect);
             break;
         case SkXfermode::kDst_Mode:
-            return fShaderA->asFragmentProcessor(context, viewM, localMatrix, fq);
+            return fShaderA->asFragmentProcessor(context, viewM, localMatrix, fq, gammaCorrect);
             break;
         default:
             SkAutoTUnref<const GrFragmentProcessor> fpA(fShaderA->asFragmentProcessor(context,
-                                                        viewM, localMatrix, fq));
+                                                        viewM, localMatrix, fq, gammaCorrect));
             if (!fpA.get()) {
                 return nullptr;
             }
             SkAutoTUnref<const GrFragmentProcessor> fpB(fShaderB->asFragmentProcessor(context,
-                                                        viewM, localMatrix, fq));
+                                                        viewM, localMatrix, fq, gammaCorrect));
             if (!fpB.get()) {
                 return nullptr;
             }