Optimize color xforms when src and dst are matching

src/core/SkColorSpaceXform.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 SkColorSpaceXform_DEFINED
 #define SkColorSpaceXform_DEFINED
 
@@ skipping 18 matching lines @@
      *  Apply the color conversion to a src buffer, storing the output in the dst buffer.
      *  The src is stored as RGBA (8888).  The dst is stored in the format indicated by
      *  |dstColorType| and is premultiplied by alpha if |premul| is set.
      */
     virtual void apply(void* dst, const uint32_t* src, int len, SkColorType dstColorType,
                        SkAlphaType dstAlphaType) const  = 0;
 
     virtual ~SkColorSpaceXform() {}
 };
 
-template <SkColorSpace::GammaNamed kDst>
+enum ColorSpaceMatch {
+    kNone_ColorSpaceMatch,
+    kGamut_ColorSpaceMatch,
+    kFull_ColorSpaceMatch,
+};
+
+template <SkColorSpace::GammaNamed kDst, ColorSpaceMatch kCSM>
 class SkColorSpaceXform_Base : public SkColorSpaceXform {
 public:
 
     void apply(void* dst, const uint32_t* src, int len, SkColorType dstColorType,
                SkAlphaType dstAlphaType) const override;
 
     static constexpr int      kDstGammaTableSize = 1024;
 
 private:
     SkColorSpaceXform_Base(const sk_sp<SkColorSpace>& srcSpace, const SkMatrix44& srcToDst,
                            const sk_sp<SkColorSpace>& dstSpace);
 
     sk_sp<SkColorLookUpTable> fColorLUT;
 
     // May contain pointers into storage or pointers into precomputed tables.
     const float*              fSrcGammaTables[3];
     float                     fSrcGammaTableStorage[3 * 256];
 
     float                     fSrcToDst[16];
 
     // May contain pointers into storage or pointers into precomputed tables.
     const uint8_t*            fDstGammaTables[3];
     uint8_t                   fDstGammaTableStorage[3 * kDstGammaTableSize];
 
     friend class SkColorSpaceXform;
 };
 
 #endif