Add SkSourceGammaTreatment enum so we know how to create mips

src/image/SkImageShader.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageShader_DEFINED
 #define SkImageShader_DEFINED
 
 #include "SkImage.h"
 #include "SkShader.h"
 
 class SkImageShader : public SkShader {
 public:
     static sk_sp<SkShader> Make(const SkImage*, TileMode tx, TileMode ty,
                                 const SkMatrix* localMatrix);
 
     bool isOpaque() const override;
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkImageShader)
 
 #if SK_SUPPORT_GPU
     const GrFragmentProcessor* asFragmentProcessor(GrContext*, const SkMatrix& viewM,
-                                                   const SkMatrix*, SkFilterQuality) const override;
+                                                   const SkMatrix*, SkFilterQuality,
+                                                   bool gammaCorrect) const override;
 #endif
 
 protected:
     void flatten(SkWriteBuffer&) const override;
     size_t onContextSize(const ContextRec&) const override;
     Context* onCreateContext(const ContextRec&, void* storage) const override;
 
     SkAutoTUnref<const SkImage> fImage;
     const TileMode              fTileModeX;
     const TileMode              fTileModeY;
 
 private:
     SkImageShader(const SkImage*, TileMode tx, TileMode ty, const SkMatrix* localMatrix);
 
     typedef SkShader INHERITED;
 };
 
 #endif