Add SkSourceGammaTreatment enum so we know how to create mips

src/effects/gradients/SkTwoPointConicalGradient.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTwoPointConicalGradient_DEFINED
 #define SkTwoPointConicalGradient_DEFINED
 
@@ skipping 42 matching lines @@
 
     private:
         typedef SkGradientShaderBase::GradientShaderBaseContext INHERITED;
     };
 
     SkShader::GradientType asAGradient(GradientInfo* info) const  override;
 #if SK_SUPPORT_GPU
     const GrFragmentProcessor* asFragmentProcessor(GrContext*,
                                                    const SkMatrix&,
                                                    const SkMatrix*,
-                                                   SkFilterQuality) const override;
+                                                   SkFilterQuality,
+                                                   bool gammaCorrect) const override;
 #endif
     bool isOpaque() const override;
 
     SkScalar getCenterX1() const { return SkPoint::Distance(fCenter1, fCenter2); }
     SkScalar getStartRadius() const { return fRadius1; }
     SkScalar getDiffRadius() const { return fRadius2 - fRadius1; }
     const SkPoint& getStartCenter() const { return fCenter1; }
     const SkPoint& getEndCenter() const { return fCenter2; }
     SkScalar getEndRadius() const { return fRadius2; }
     bool isFlippedGrad() const { return fFlippedGrad; }
@@ skipping 12 matching lines @@
     SkPoint fCenter2;
     SkScalar fRadius1;
     SkScalar fRadius2;
     bool fFlippedGrad;
 
     friend class SkGradientShader;
     typedef SkGradientShaderBase INHERITED;
 };
 
 #endif