(Some) gradients are gamma and gamut correct on GPU

include/gpu/GrColorSpaceXform.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrColorSpaceXform_DEFINED
 #define GrColorSpaceXform_DEFINED
 
 #include "GrColor.h"
 #include "SkMatrix44.h"
 #include "SkRefCnt.h"
 
 class SkColorSpace;
 
  /**
   * Represents a color gamut transformation (as a 4x4 color matrix)
   */
 class GrColorSpaceXform : public SkRefCnt {
 public:
     GrColorSpaceXform(const SkMatrix44& srcToDst);
 
     static sk_sp<GrColorSpaceXform> Make(SkColorSpace* src, SkColorSpace* dst);
 
-    const SkMatrix44& srcToDst() { return fSrcToDst; }
+    const SkMatrix44& srcToDst() const { return fSrcToDst; }
 
     /**
      * GrGLSLFragmentProcessor::GenKey() must call this and include the returned value in its
      * computed key.
      */
     static uint32_t XformKey(GrColorSpaceXform* xform) {
         // Code generation changes if there is an xform, but it otherwise constant
         return SkToBool(xform) ? 1 : 0;
     }
 
+    static bool Equals(const GrColorSpaceXform* a, const GrColorSpaceXform* b);
+
     GrColor4f apply(const GrColor4f& srcColor);
 
 private:
     SkMatrix44 fSrcToDst;
 };
 
 #endif