Add SkSourceGammaTreatment enum so we know how to create mips

gm/dcshader.cpp

Index: gm/dcshader.cpp
diff --git a/gm/dcshader.cpp b/gm/dcshader.cpp
index e402fc0c2b7ee69ea62749a2806b9383e5ee1d80..6c73bdc181e68bb009399bf1166ff8edb4bdcef4 100644
--- a/gm/dcshader.cpp
+++ b/gm/dcshader.cpp
@@ -38,7 +38,8 @@ public:
     const GrFragmentProcessor* asFragmentProcessor(GrContext*,
                                                    const SkMatrix& viewM,
                                                    const SkMatrix* localMatrix,
-                                                   SkFilterQuality) const override;
+                                                   SkFilterQuality,
+                                                   bool gammaCorrect) const override;
 
 #ifndef SK_IGNORE_TO_STRING
     void toString(SkString* str) const override {
@@ -101,7 +102,8 @@ private:
 const GrFragmentProcessor* DCShader::asFragmentProcessor(GrContext*,
                                                          const SkMatrix& viewM,
                                                          const SkMatrix* localMatrix,
-                                                         SkFilterQuality) const {
+                                                         SkFilterQuality,
+                                                         bool gammaCorrect) const {
     SkAutoTUnref<const GrFragmentProcessor> inner(new DCFP(fDeviceMatrix));
     return GrFragmentProcessor::MulOutputByInputAlpha(inner);
 }