Add SkSourceGammaTreatment enum so we know how to create mips

src/core/SkComposeShader.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkComposeShader_DEFINED
 #define SkComposeShader_DEFINED
 
@@ skipping 20 matching lines @@
     SkComposeShader(sk_sp<SkShader> sA, sk_sp<SkShader> sB, sk_sp<SkXfermode> mode)
         : fShaderA(std::move(sA))
         , fShaderB(std::move(sB))
         , fMode(std::move(mode))
     {}
 
 #if SK_SUPPORT_GPU
     const GrFragmentProcessor*  asFragmentProcessor(GrContext*,
                                                     const SkMatrix& viewM,
                                                     const SkMatrix* localMatrix,
-                                                    SkFilterQuality) const override;
+                                                    SkFilterQuality,
+                                                    SkSourceGammaTreatment) const override;
 #endif
 
     class ComposeShaderContext : public SkShader::Context {
     public:
         // When this object gets destroyed, it will call contextA and contextB's destructor
         // but it will NOT free the memory.
         ComposeShaderContext(const SkComposeShader&, const ContextRec&,
                              SkShader::Context* contextA, SkShader::Context* contextB);
 
         SkShader::Context* getShaderContextA() const { return fShaderContextA; }
@@ skipping 28 matching lines @@
 
 private:
     sk_sp<SkShader>     fShaderA;
     sk_sp<SkShader>     fShaderB;
     sk_sp<SkXfermode>   fMode;
 
     typedef SkShader INHERITED;
 };
 
 #endif